J . Linn. SOC.(Bot.),60, 383, p . 381
With 3 plate8 and 6 text-figure8
Printed i n Great Britain
February, 1968
38 1
Evolution in Spartina (Gramineae)
11. Chromosomes, basic relationships and the problem of
S. x townsendii agg.
BY C. J. MARCHANT
Jodrell Laboratoy, Royal Botanic Gardens, Kew, Surrey
(Accepted for publication June,1967)
Communicated by the Botanical Editor
An intensive study of the cytology and sexual behaviour of the classical Spartinu x townaendii
agg. and their putative parentsin southern England reveals a more complex chromosomal situation than had previously been reported, including aneusomaty in SouthamptonS. alternijlora
populations and in 8. x towmendii agg. Chromosome numbers are 2n = 60 and 2n = 62 for S.
muritima and S. alterniflora respectively and 2n=62 and 2n= 120, 122 and 124 (chromosome
races) for S. x townaendii Fi and Amphidiploid derivatives respectively. These numbers,
though their summation is leas precise than hitherto reported, still support the hybridity and
amphidiploid origin of S. x toumsendii egg. and the process is further confirmed by meiotic
pairing data and the discovery of wild bmkcross hybrids (2n=c.90 and 2n= 76)near the site
of origin at Southampton. The 2n = 62 chromosome number ofS. alternaflora,out of line with the
z= 10 base number of the genus, is explained tw a polysomic condition (2n= 60+ 2 ) and needs
further investigation with a study of North American populations.
It is suggested that Chromosome races found in S. x townsendii Amphidiploid will provide
adaptive variation in this highly significant and successful amphidiploid.
INTRODUCTION
The evolutionary problems associated with Spartina x townsendii have been outlined in
the introduction to the initial paper of this series (Marchant, 1967). Although morphological and historical data support the hybrid origin of S. x t m e n d i i and its amphidiploids (Marchant, loc. cit.), the evidence is not decisive. Further evidence is now available
from fundamental chromosome studies of the ‘S.x townsendii complex ’ (Marchant,
loc. cit.), which includes those species considered to be directly involved in the origin of
S. x townsendii, namely S.maritima and S.alterniflora. These species, withS. x townsendii,
its amphidiploids and other derivatives form the Spartina flora of the British salt marshes
centred on the Hampshire basin. This paper examines the cytological interrelationships
of the British Spartina species and hybrids within the complex.
MATERIAL AND METHODS
A list of plant materials and localities are included in the Appendix, and morphological
information corresponding to many of the accessions has been tabulated previously
(Marchant, 1967). Voucher specimens of chromosome-counted material will be deposited
in the Kew Herbarium.
There are considerable technical difficulties in handling the small Spartina chromosomes
and this has meant that relatively few accurate counts have been made (Table 1). The
25
c. J. - C U T
382
mitotic index of root tips is low, particularly in Amphidiploids, and a tough root cap
reduces penetration of pretreatment chemicals and impedes cell flattening. Leaf primordia
often give preparations superior to root tips.
The most satisfactory schedule found for somatic chromosome preparation is as follows:
(1) Pretreatment of excised root tips or dissected apices in water at 1"-3"C for 12 h
followed by 2-3 h in alphabromonaphthalene (abn).
(2) Feulgen staining after 14 min hydrolysis is far superior to orcein.
(3) Several hours digestion in 3% pectinase solution at 30"C, to soften the roots
before squashing.
For meiotic preparations inflorescences were fixed in 6 :3 :1 Carnoy (propionic acid)
fixative (adding 1 ml of ferric chloride or ferric acetate solution) and stored at -20°C for
at least one week before staining with the standard propionic carmine bud squash technique. Stickiness was encountered in the two backcross hybrids (and sometimes also in
the species) so that well-spread metaphases were rarely obtained.
Experimental hybridizations were made by isolating heads inside cellophane bags.
Emasculation was not done but the two inflorescences in each cross were chosen at
different developmental stages to give maximum chance of crossing. Harvested seed
germinated successfully in sandy soil, the process being more even and rapid after storage
for 1-6 months in a moist dark atmosphere at about 1°C.
CHROMOSOME NUMBERS, CHROMOSOME PlLIItING AND FERTILITY
At meiosis the accurate determination of chiasma frequency in species with such small
chromosomes is difficult but, since chiasmata seem rarely to exceed one per chromosome
arm, approximate values could be scored from ring and rod bivalents.
During division in pmds of 8. maritima and the hybrids, one or more small spherical
bodies usually occur in the cytoplasm (their position is indicated in some figures),which
are persistent nucleoli whose behaviour will be described elsewhere.
1. The cytobqy of th 'S. x townsendii'complex
(a) S. maritima
This is one of the putative parents of 8. x toumsendii and is the only Sprtina species
native to Europe. Precise chromosome counts of 2n=60 were obtained for six British
populations (Pl. 1, fig. 1 and P1.2, figs 1 and 2) and an approximate count of 2n=60 for
another (526).
The chromosomes were usually associated at meiosis as 30 bivalents (Pl. 2, fig. 1 and
Table 1) with rarely a low frequency of univalents and a chiasma frequency of 0.92 per
paired chromosome. The polar (centromeric)ends of some ring bivalents were indented
giving them a double-ended appearance which can just be seen in one or two bivalents of
fig. 1 in P1.2, and in Text-fig. 1. These are reminiscent of a quadrivelent (Text-fig. I), but
there is no evidence either from size comparisons or from anaphase separation (Pl. 2,
fig. 2) that these 8. maritima structures are associations of more than two chromosomes.
The appearance could be an artifact of fixation but it may be that in these small metacentrics proximal chiasma formation, by bunching the free distal ends of the arms close
together (Text-fig. l ) ,could produce the double appearance and would also explain the
slight lagging observed in some bivalents at first anaphase. Alternatively, neocentric
activity of the kind described by Prakken & Muntzing (1942)in rye may be present in the
ends of the 8.nzaritima bivalent arms again resulting in the double-endedappearance.
High values obtained for mature pollen stainability in three populations (Table 2)
contrtlsted with a low seed-set;a total sample of 1860 spikelets from four populations and
an artificial cross between two of them contained only 174 partially-filled grains, of which
'
Plant
62
62
60
24
57
56
I
2.2
(0-12)
0.58
(0-4)
0.30
(04)
4.8
6.4
4.5
(0-13)
Rod
25-1
23.4
25.3
(19-30)
Ring
29-8
(26-31)
29.9
(29-3 1)
29.8
(28-30)
Total
i.e. number of cells with 1 or with 2 trivalent8 (111)or with 1 quadrivelent (IV).
* Lower number in parentheses is the range per cell.
(N. Hythe)
S9b
(Marchwood)
s9S
S. allernifEota
s21, S23 and ,940
S. maritima
Chromosome No.of
no. (2n)
Oelh
11
2
2
0
0
1
0
2
0
1
with
&
1
IVt
cells
IIIt
G3b
with
Mean metaphese pairing per cell*
0
%
Cellswith
rnultivalenta
Table 1. S. maritime and S. alterniflora-chronzosome pairing at metaphase Z
0.90
0.89
0-92
per
Pd.
chr.
55.6
54.2
55.2
per
pmc
f’
w
m
w
v
$
Q
A
s-
384
C.J. MARCHANT
4
t
t
Evolution in Spartina (Gramineae)I I
385
t
+
Text-fig. 1. Explanation of the ‘double-ended’metaphase bivalents in S. ntaritima pollen
mother cells. Arrows indicate spindle axis. a, Camera lucida drawing of normal and ‘doubleended ‘ bivalents. b, Hypothetical zigzag and ring quadrivalents. C, Diagram of proximal
chiasmate (i) and (ii) in a bivalent. d, Hypothetical drawings of bivalents resulting from
proximal chiasma formation and fully spiralized chromosome arms.
3% germinated (Table 2). Germinajion of 521 pollen on collodion membranes (Savage,
1957) was poor, with about 10% growing a short tube.
(b) 5. alterniflora
Root counts of 2n=62 (Pl. 1, fig. 2) were obtained from plants in the only three relic
localities (two now extinct) of this species in Britain, in Southampton Water, and in a
clone from the St. Lawrence River, Quebec, Canada and another from Woods Hole,
Massachusetts (Marchant, 1968).
Inconstancy of somatic chromosome number was found in some tillers of a British
population (Clone S9a). with a range from 61 to 66 around a mode of 62 in a single tiller,
probably correlated with other mitotic abnormalities observed in 28 yo of non-pretreated
tillers, such as fragments, laggards, a dicentric bridge (Pl.1, fig. 3) or cytoplasmic chromatin
a t interphase. Significantly these abnormalities occurred in plants with weak growth. At
meiosis in all plants chromosome counts were constant a t 62 and no additional or deleted
chromosomes were observed. In populations S9a and S9b there is often complete pairing of
31 bivalents (Pl. 2, fig. 4) with a chiasma frequency between 0-89 and 0.90 per paired
chromosome respectively (Table 1) but 60% of pmc’s have a low frequency of minor
spikelet
sample size
Percentage
seed sett
srains
Sample sits
Percentage
stainable
630
48.7
462
66.4
6608’
0
60
0
(8)
Hythe
(b)
t
S9b (Hythe)
Hythe
-
-
22-0
0
moo+
26.1
618
site’
100
‘Low
site’
-
41.7
673
0
0
34
32-1
64.9
17,900
614
J
616
R
(‘High’)
R
(‘High’)
898 wood)
s. altemipma--fresh materid
‘Low
* All field samples.
t Fertility could not be tested in the absence of d.
seed
Pollen*
Clone or locality
Population
Species and source
of material
A
-
-
0.0
423
Table 3. Fertility dcctafor S.a l t e d o r a
0
0
66
24.6
56
368
1961
S!bK
-
89b x S9aD
-
D
1
4-28
1838
91%
Bmmfield
.
2.87
766
Hythe
1879
Gmvea
Dried herbarium matarid
I
3
!
F
9
9
Far out
Middle
Inshore
Inshore
Inshore
Middle
B
H
K
R
S9b
Medium
Medium
High7
LOW
Low
Medium
Low
Level
t Small tussocks or 'mud islands'.
J
Inehore
Situation
A
S9a
Population
or clone
Poor
Fair
Verygood
Rather
Poor
Poor
Poor
Poor
Drainage
at low tide
Site conditions
Good
Robust and
vigorous
Moderate
Weak and
short
Healthy and
vigorous
Fair
Fair only
8PP-m
external
Vigour of
P h t
a
d by
Variabl-some
6xations irregular
some mainly regular
Often with extreme
irregularities
u p to 20%
irregular
Mainly regular
50 yo irregular
Sometimes extreme
irregularities
Many irregular
Many irregular
Meiosis: assessment
of normality
Many dehisced
Not
Some dehisced
Many dehisced
AU dehisced
78
{:;
Many dehisced
None dehisced
45
assessed
None dehisced
Anther
condition
100
(%I
Aborted
pollen
Table 4. Relationship between environment and fertility in S . alterniflora
09
4
w
388
c.J. - C U T
irregularities in the form of univalents, multivalents and heteromorphic bivalents. In
view of the chromosome number of 2n=62, an observed maximum of two multivalents
(trivalents or a quadrivalentTable 1) would seem to be correlated with the two chromosomes additional (60+2) to the expected bmic polyploid level of 2n = 60, and suggests a
polysomic condition.
At stages following MI, many pmc’s behave normally while others have extreme
irregularities and fragmentation (Pl. 2, fig. 6), often in the same inflorescence or anther
as the normal cells. The cause seems to be correlated with physiological rather than
genetic disturbances, indeed many plants in the two wild populations are unhealthy or
moribund, sometimeswith disetlsedleaves. There is great variation in marsh physiography
in the areas where these populations grow, elevated well-drained sites (R) alternating
with low-lying waterlogged sites (L). Table 4 is a summary of a preliminary survey which
shows good correlation of elevation and drainage with plant vigour but not with meiotic
behaviour and pollen fertility. The latter is very variable (Table 3), with a range from nondehiscent to fully dehiscent anthers. Artificial pollen germination failed but functional
pollen was occasionally indicated by natural germination in non-dehisced anthers.
Caryopses do not develop in the field or in artificial pollinations (Table 3).
(c)
S. x townsendii B1
One clone (544)from Hythe near Southampton had a precise somatic number of 2n = 62
(Pl. 1, fig. 4) and all others had approximately 2n=62. In a few clones (see Appendix)
slightly variable numbers were found in the tiller apex (cf. S . alternijlora)and frequently
analyses of pollen mother cell first metaphases revealed variation in adjacent pmc’s
(Table5),illustrated in P1.2, figs 7 and 8, while others had, by contrast, a constant number
of 2n=62.
No F1 hybrids having a 2n chromosome number of 61 (expected from a cross between
the two putative parents) have been detected, but the polyhaploid seedling described in a
previous paper (Marchant, 1967), which appeared in the progeny of a 2n= 122 Amphidiploid clone, had 2n = 61.
Meiotic behaviour is complex in all clones of this sterile material and somewhat variable
(Table5 ) .How much of this variability parallels morphologicaldiversity (Marchant, 1967)
and indicates plants of different genetic constitution and hence of separate origin is
difficult to determine. Some F1 clones of differing morphology lose their differences in the
more uniform environment of cultivation (S44,S7 and 535 from the classical Hythe area
of original PI) whilst others, such as the diminutive 519 ‘Dwarf Brown’ from Wales
(a phenotype first recorded by Chater & Jones, 1961) remain morphologically distinct and
also have a much higher level of meiotic pairing (Table 6).Chiasma frequencies range from
0.53 to 0.75 per paired chromosome and from 17.4 to 31.3 per cell; the latter a reflection of
the differences of univalent frequency. Some of these plants may be of different origin ;by
hybrid parthenogenesis or from the twin seedlings known to be occasionally produced by
the Amphidiploid (Marchant, 1967).
Plate 2, figs 7 and 8 are typical first metaphases. Despite numerous univalents and
multivalents, pairing is comparatively high with about half or less of the total complement
left unpaired. Trivalent8are most common, quadrivalents frequent and occasionally there
are more complex associations. Dicentric inversion bridges and fragments occasionally
occur at anaphase. Sometimes rod bivalents are very attenuated indicating a reduction of
spiralization (cf. Hair, 1956, on Agropyron) probably influenced by the hybrid genotype.
Non-chiasmate associations of univalents in the cytoplasm are frequent (Pl. 2, fig. 8),
similar to the case reported in rye by Ostergren & Vigfussen (1953).
An occasional pmc was almost completely asynaptic and others contained about double
the normal complement, e.g. an anther of S44 (2n=51-69) contained two cells with
2n = 84 and 2n =94, respectively, and a third with two very unequal spindles and about
22
19
12
10
7
50-64
49-62
56-64
62
102
51-69?
(-118)
62
Chromosome
no. 2n
32.2
(21-47)
27.9
(14-35)
28.3
( 19-51)
22.6
(19-31)
19.0
(14-23)
23-7
( 19-30)
I
8.6
10.0
7.6
8.6
10.7
9.3
Rod
c
3.0
6.3
4.7
2.9
3.8
3.5
Ring
I1
,
11-6
16-3
12.3
11.5
14.5
12-8
Total
3.6
2.8
2.6
1.5
1.4
0.61
I11
0.43
0.30
0.17
0.26
0.22
0-26
IV
6 I11
+ 1 IV
6 IIIf
+ 1 IV
3 I11
+ 1 IV
5 1118
+ 1 JY
4 III*
5 I11
Max.
multivs.
per
cell
28.0
(12-40)
32.8
(2243)
28.54
(6-43)
33.3
(27-42)
42-2
(38-50)
42.0
(41-43)
Mean
paired
chr. per
cell
f A V in three cells.
t To avoid confusion those few cells with abnormal chromosomenumbers above 2n= 69 omitted from analysis.
* A V in one cell.
s44
(Hythe ‘Normal’)
s7
(Hythe ‘Dward’)
s35
(Hythe ‘Giant’)
H20
(Hayling)
s19
(Dovey ‘Dwarf’)
BR4
(Somerset)
Plant
No.
of
cells
Mean metaphase pairing per cell
Table 5. S . x townsendii F1 hybrid-chromosm pairing at mdaphase I
17.4
17.4
0.53
0.53
0.75
0.72
0.68
31.3
30.6
23.6
18-7
18.1
18.1
0.65
0.65
0.65
per
pmc
per
prd.
chr.
Mean
chiasmata
Y
f‘
$
Q
h
P
9B$
rn
m
f’
S’
f
h
d
124 chromosomes. These probably result from pre-meiotic apindle failure and would give
unreduced gametes but they have not been observed in su5cient numbers to make anther
dehiscence possible.
At the tetrad stage the pollen always aborts and seed is apparently never formed even
under heavy pollination from the Amphidiploid or parental species.
(d) S. x townsendii Amphidiploid
Preparations adequate for accurate somatic counts have seldom been obtained (Pl. 1,
fig. 6).Amongpmc's from the same anther there is a small, distinct variation in chromosome
number and although this is confined within fairly narrow limits in a given plant the range
differs from one clone to another and some show no such variation.
I2r
I
s 20
L1
40
35
-
30
-
25
-
20
-
I5
-
-
B
5 4
2
2
11
J
12[,
10
4
2
T5
iL
TI1
5
0 :g!Gg
2n chromosome number
Text-fig. 2. Amphidiploid chromosome number analysis at meiotic metaphase I. (For further
explanation see text.)
25
45
76
20
c. 90
Also one cell with one VI.
642
(South Hythe)
S31F
(South Hythe)
(2) Backcrosses
c. 124
122
520 and E6
14
17
120-124
(Hants)
T10
(EM4
30
120-127
Chromosome
no. 2n
(1) Amphidiploids
L1 and T6
(Hants)
RB (Hants.)
Plant
No.
of
Cells
8.5
2-16
11-8
4-1 9
2-2
0-8
0-10
0-8
3-8
0-7
5.3
2.0
I
7.0
4.9
24.6
35.9
43.5
35.2
21.5
16.4
39.9
28.8
17.9
27.8
I1
40.8
37-45
31.6
21-36
56-4
49-61
57.8
55-60
56.6
5M1
59-9
54-63
7
3
0
0
1
1
4
5
1*
8
8
8
1
0
0
0
0
1
1
0
0
0
6
3
0
0
16
20
1
30
50
59
70
1
0
0
0
0
0
0
0
2
Cells
with
\
7 multivs.
R o d R i n g T o t a l 1 2 3 4 5 V
( %)
Frequency of
IV or III+I.
No. of cells with
Mean metaphase pekhg per cell
0.0
33.3
25.0
21-4
( %)
Iv
Zigzag
Table 6. Chromosomepairing at m e t a p h e I-Amphidiploids and backcrossm
82.2
74-90
58-6
42-70
118.3
112-122
118.0
113-120
116.8
112-122
121.3
116-126
Mean
paired
chr. per
cell
0-88
0.94
0.84
0.74
51.2
77.4
121.8
87.9
2
3I%!
xti'
392
C. J. MARCHANT
Numerical variation in 12 clones is summarized as pooled data in the large histogram in
Text-fig.2 together with examples of individual clones. The bivalent8 are variable in size
so that one has to be cautious in distinguishing any univalents, and they sometimes have
the double-ended appearance described earlier for 8.m r i t i m a . Only the most definite
counts from this diacult material are included in the data of Text-fig. 2.
Five clones (W2, H2, S20, DOV.6, E6) apparently do not have aneusomaty at meiosis
(see Appendix) and their chromosome numbers are all even-numbered with 2n = 120 in
W2 and 2n= 122 in the other 4 clones. Each of the 7 aneusomatic plants included in the
data of Text-fig.2 is seen to have a modal number which may be 120,122,123 (Ll)or 124
and a small range of variation from 120 to 127. Meiotic complements from both aneusomatic and normal plants are shown in P1.3.
The tendency in aneusomatic plants to bimodality and to a higher frequency of evenrather than odd-numbered cells (Text-fig. 2) is no doubt linked with the nature of premeiotic errom (Pl. 1, fig. 6); the failure of division and lagging of one chromosome at
mitotic metaphase and its incorporation entire in one of the daughter nuclei will mean a
difference between daughter cell complements of not one but two half-chromosomes.
All populations on the south and west coasts of Britain showed almost regular meiotic
metaphase pairing (Pl. 3, figs 2 , 3 and 5).
The pairing data in six clones in Table 6 shows that all have a fairly high chiasma
frequency between 0.74 and 0.86 per paired chromosome,though lower than the parental
species. Secondary bivalent pairing was seen but not in suilicient pmc’s for a useful
analysis.
Univalents occur up to a maximum of 10 in some pmc’s of all populations. Some must
result from aneusomaty and a consequent lack of available homologues; others may be
due to a hindering of pairing in the crowded zygotene nucleus in these high chromosomenumbered plants. Quadrivalents (IV) or trivalents-plus-univalent8(I11 I) (a single case
of a hexivalent in RB)occur in a low frequency with a maximum of 6 in clone L1 (Textfig. 3). The percentage of cells having IV’s is highest in the 2n= 120 clones (60-70%) and
lowest in the 2n=c. 124 clone (30%). The Qause of this difference is obscure but multivalent pairing may well be subject to genetic control and morphological evidence of
variation (Marchant, 1967) shows that genetic make-up does differ in these outcrossing
Amphidiploids.
Data for pollen and seed in field samples (Table 7) reveal high fertility. Potted plants,
while maintaining high pollen values, have a much wider range of seed set (4-88%),
mostly less than 30%, perhaps due to the relatively dry atmospheric conditions in the
greenhouse at the peak time of flowering (early autumn), or the absence of natural windpollination.
+
(e) Backcroa8 hybrid8
Two Sprtina clones found in Southampton Water differed widely in chromosome
number from the species and hybrids already described.
(i) CloneS42. No somatic counts were obtained but the plants had the unusual number of
2n=c. 90 in meiotic metaphaae (Text-fig.4).
Table 6 and Text-fig. 4 show the typical irregularity and stickiness in pmc’s of this 90chromosome clone which makes complete pairing analysis very difficult. Univalents are
always present with a maximum of 16 (mean of 8.5 per cell). Multivalents are infrequent,
the maximum being a trivalent or quedrivalent per cell and rarely a pentavalent. The
chiasma frequency of 0-94(Table 6) is higher than the Amphidiploidsand equivalent to the
species. There is relatively little lagging a t anaphase. Second division is also more or less
regular and tetrads appear normal. Pollen stainability (Table 7) is about 90%, while
abundant seed is set.
(ii) Clone S31F. Counts of 2n=76 and c. 76 were obtained from root tips and tiller
germinated
seed
Sample size
Percentage
stainable
grains
Spikelet
sample size
Percentage
seed set
Total seed
sown
Percentage
84.6
250
44
-
-
100
38
775
-
1031
95-7
227
80.6
mls
60.0
7000
-
-
53
3!$
X':
XZ
3 s
32
?:g
( ) =actual number germinated
28
100
18.7
362
1311
87.5
m 3
s!$
u1;
XX
Y
* =all data were collected from populations in the field
and
fertility
Seed set
Pollen
fertility
Clone or locality, etc.
S317
33
150
20.0
720
-
-
R
X
55'
L99
ul
S34(2)
Population
S34(1)
Amphidiploids*
Species or hybrid
48
150
78-7
534
-
5
r
Y
3
5'
L1
Table 7. Fertility data for Amphidiploids and backcrosses
11.5
(9)
78
15.8
495
842;
18.4
c
-
-
-
0.0
396
1273
73.1
-
-
1141
57.8
1961
S31F (2n=76)
Backcross hybrids
-
-
-
-
1370
54.9
1962
394
4
Text-flg. 3. S. x townaendki Amphidiploid (clone L1) meiosis. 2n= 120. Metapheee I. 6 IV
(amwed) 49 I1 2 I.
+
+
I
0
6
Text-fig.4. Backcross hybrid (clone842) meiosis. 2n=o. 90. Metapham I. 1 IV+ 38 11+ 12 J.
a
10P
t
8
Text-Ag.6. Backcrosshybrid (done 831F)meiosis. 2n= 78. MetaphamI. 1 IV + 1 I11 + 30 11
9 I.
I
+
Evolution in Spartina (Graminme)11
395
apices (Pl. 1, fig. 7) respectively. The few meiotic cells free of stickiness have 2n=76
(Text-fig. 5 and Table 6).
Forty-five meiotic metaphases approximately analysed have up to 19 univalents per
pmc (mean of 1 l e a ) , nevertheless chiasma frequency is high (0.88per paired chromosome)
owing to a preponderance of ring bivalents. There are also occasional multivalents
(Table 7 and text-fig. 5).At anaphase between 3 and 11 univalents lag and are not included
in daughter nuclei. Up to six anaphase bridges occur, some of which may be stretched
bivalent arms having ‘sticky ’ ends ; others result from delayed chiasma separation and
despiralization (Hair, 1956). However, some a t least are dicentric with 1 4 fragments
indicating inversion hybridity.
Sixty-five per cent of telophase cells have bridges and relic (broken) bridges, fragments
or cytoplasmic chromatin, also some paler staining bodies which may be nucleolar
material. ‘Tetrads ’ are very irregular with micronuclei, microcytes (56.5 yo),diads, triads
and pentads. There is a very noticeable annual variation in pollen stainability (Table 7)
in the field, while in pot-grown plants there is greater stability. The 1962 sample with
54.9 yo stainability was tested for germination in a sucrose plus boric acid hanging drop
(Vmil, 1960) and 20.8 yo of sound grains grew pollen tubes. Anthers always dehisce and
some seed is formed (Table 7) but this is of low viability (116%). One seedling survived
long enough for a chromosome count to be made (2n = c. 78), but none grew t o maturity.
(iii) Clone S31H. Morphologically very similar to S31F and somatic chromosome
preparations gave a count of 2n = c. 75.
(f) Chromosome number and kayotype rehtiomhips within the complex
When the corrected numbers of the putative parent species (S.maritima and S. alterniflora)and of the hybrids are arranged schematically, as illustrated below, they accord
quite well with the supposed hybrid origin of S. x towmendii, but the 2n = 62 number of
the F1 closely resembles but does not exactly correspond with the expected number for
this hybrid, namely the sum (61) of the gametic numbers of the two parental species:
8.mariti2n = 60
(56)*
x
8.alterniJEora
i
2n = 62
(70)*
8.x townsendii F1
2n = 62
Amphihploids
2n = 120,122,124
(126)*
* Huskins’ (1931) Chromosome numbers.
An attempt was made to corroborate this hypothetical relationship of chromosome
numbers in more detail by a karyotype analysis. Micrometer eyepiece measurements of
the somatic chromosomes were categorized into three arbitrary classes of length (Table 8).
A fairly distinct relationship exists between the complements of the two species and the
hybrids which is particularly precise in the ‘long ’ (L) chromosome category, the summation of gametic numbers in S. mritima and S. alterniflora (viz. 4L+6L) equalling the
somatic number (1OL) in S. x towmendii F1. The Amphidiploid (2n= 122 and 124) has, as
would be expected, twice the number of L’s as in the Fr. Numbers in the other two
categories, though more difficult to estimate and less precise, are quite close to the expected
summation. The alternative hypothesis of straight chromosome doubling (i.e. auto-
396
tetraploidy) from either species is not strictly supported by the numbers in each category,
but S. alterniJlora confoirns fairly closely and this possibility cannot be ruled out completely.
Table 8. Somatic chromosome analysis
2n somatic complement-numbers of
chromosomes in three categories*
Plant
s. mritima
S. alterniflora
S. x townaendii
F1 hybrid
S. x tmnaendii
Amphidiploid
’sea text.
L
M
Chromosome
no. 2n
(‘long’)
(‘intermediate’)
S
(‘short’)
No. of
cells
00
62
8
12
36
30
I0
20
13
11
02
(01)
10
(10)
34
(33)
18
(18)
9
124
122
(122)
20
20
(20)
64
60
(66)
40
42
(30)
2
1
Numbers in parentheses are the expected vdues, bawd on parental numbers.
2. Theproblem of laboratory synthesis of F1 and amphidiploid
Attempts were made to simulate the origin of S. x townsendii and to vindicate relationships between it, the amphidiploid,and the presumed backcrosses, by selective hybridizations.
Many culms (totalling over 200 receptive spikelets) of S. alternijZora were bagged with
pollen-bearing S. maritima and in addition a large number of culms of these two species
were left to interpollinate freely by placing pots adjacent to each other. In neither method
nor in reciprocal crosses was any seed set.
In crossesbetweennatural backcrosses S31F (an= 76) and S31J with S. maritima (521)
as male, one seed was set on S31J and successfully germinated but died in a juvenile
condition. In reciprocal crosses of the same, relatively much more seed was set, i.e. 39 in
777 spikeletsor 6.63 yo.This evidence of pollen fertility in the 2n = 76 backcross prompted
attempts to cross it as male to S. alterniJlora but without success.
A backcross of S20 (Amphidiploid)pollen to S. maritima (524) failed, as did open
pollination of S. alternijZora with Amphidiploid.
Potted alterni$ora and mritima floweringamidst abundant pollen from Amphidiploids,
S. glubra and backcrosses in the experimental garden, failed to set any seed. However,
S.maritima seemed to offer less of a barrier to cross pollination for, besides its seed set with
the S31F and J backcrosses, this species showed considerable seed set with S. glabra and a
little ins. maritima x maritima crosses (Table3))especiallywhen these were made between
geographically isolated populations (presumably different genotypes).
Caution is necessary in drawing conclusions from these crosses attempted under
artificial conditions. The necessary environment was perhaps not achieved in the experimental gardens and really favourable crossing conditionsmay be limited to the salt marsh
environment, and then rarely. Field experiments were beyond the scope of the investigation but a solution might be to transplant S . matitima plants into the natural alterniJlora
populations, and vice versa, and study the results of interpollination.
Chromosome doubling experiments have been carried out successfully using spindleinhibitors (colchicine)with a number of grass genera (e.g. Sears, 1939; Bell, 1950; Borrill,
1963). Chromosome doubling was attempted in F1 hybrid S. x townsendii and in the two
parent species in order to compare the resulting polyploids with wild amphidiploid plants
Evolution in Spartina (Gramineae)I I
397
and hence confirm the constitution of the latter. The complete sterility ofS. x townsendii F1
prevented the use of the seed treatment techniques of Johnson 6 Holtz (1946)and left the
alternatives of meristematic treatment in the tiller apices to induce tetraploid shoots or
treatment of mitotic cells in the floral parts just prior to pmc and egg cell formation to
induce doubled gametes, both of which were unsuccessful.
The negative results suggest that in Spartina the chemical solutions do not readily
penetrate to the meristems and also that the plant is highly resistant to colchicine effecte
or a t least, it seems difficult to induce ‘tetraploidy’ in sufficient meristematic cells to
compete with normal ‘diploid’ cells.
Experiments are continuing with colchicine and other techniques, such as temperature
shock (Randolph, 1932; Sax, 1936; Dermen, 1938) and chemical treatment. If chromosome-doubled plants can be synthesized they will provide a most informative comparison
with wild populations of S. x t m e n d i i agg.
DISCUSSION
1 . Basic chromosome number
The chromosome numbers of S. maritima populations reported here and those of other
Canadian, American and Atlantic Island species (Marchant, 1968), namely 2n=40 and
2n = 60, suggest that the basic number is x = 10. Nevertheless, a n anomaly remains in the
chromosome numbers of S.alternijlora and S . glabra, since both have 2n =62. These species
are closely related and have a very wide distribution in the Eastern United States and
Canada yet all clones so far counted have the 2n number of 62 and in most cases a regular
meiosis. How then are we to explain this difference in chromosome number from other
species?
As a near-multiple of 7 it might be argued that 2n = 62 is a near-nonaploid on the old
basic number (x= 7 ) ,but there is little evidence in S.alterni$ora and none in S. glabra for
extensive irregular pairing which would be expected within the additional set a t meiosis.
An alternative to the 9x concept is a base of 31 but this presupposes a n unlikely evolutionary step involving the disruption of the six basic chromosome sets of the 2n=BO
species and their re-organization into two sets of 31. It is far more logical to assume that
four basic sets of 10 remain undisturbed while the other two have increased ( l o + 1 ) either
by splitting of metacentrics into telocentrics or by reduplication giving tri- and tetrasomics. Since the chromosomes are too small for a precise karyotype analysis, evidence
for polysomy can only be indirect and the observed multivalent pairing a t meiosis could
be due entirely to structural re-arrangements in the chromosomes.
As another alternative, the meiotic abnormalities may result, not from polysomy, but
from inbreeding, which is known to cause similar effects in rye (Rees, 1965).This suggestion
is supported by the present isolation of the 8.alterni$ora genotypes remaining in Britain,
which may thus have been forced into inbreeding.
Nevertheless, the nature of the multivalent pairing makes polysomy more plausible
and the maximum frequency of two trivalents which occurs a t meiosis in both populations
of 8.alterni$ora strongly suggests trisomy, the two additional chromosomes retaining
sufficient homology with one or two pairs (tri- or tetrasomy) in the complement to form
occasional multivalents.
The presence of quadrivalents in the same anther as pmc’s with two trivalents or
complete bivalent pairing may mean a more complicated arrangement, perhaps as a
result of the polyploid ( e x ) nature of this species. As a further complication, heteromorphic bivalents were observed. This suggests that unequal translocation occurred
between the two trisomic sets so that bivalents, quadrivalents or larger configurations
are now possible as in an interchange heterozygote.
Whatever detailed conclusions can eventually be arrived a t from these data after
20
398
c. J. U
m
T
further investigation, polysomy is clearly the most plausible explanation of the two
chromosomes in excess of the diploid number of 2n =60.
2. C h r m s m e number uarktion within plants
Variation in chromosome number occurs within the tissues of some plants of all members
of the 8.x t m e n d i i complex except 8. maritima. The variation could be explained by
the existence of B-chromosomes. These are tlow known to be common in many plant
genera (Darlington& Wylie, 1966) and particularly in grasses for example Poa (Muntaing
& Nygren, 1966), Anthmnthum (Ostergren, 1947), and Dactylk (Jones, 1962) and their
numbers in individual pollen mother cells can be large and variable (Frost, 1948). Within
8partdna, 8. pectinata from Canada has obvious B-chromosomes distinguished by smaller
size than the A-chromosomesand by different meiotic behaviour (Marchant, 1968) and
they have been previously reported in this and one other species (Avdulov, 1931). In
8.townsendid,where the largest variation in chromosome number occurs, the variation is
always in excess of a well-defined minimum level (usually 2n=120) in each clone; a
situation which is suggestive of supernumerary chromosomes.
Against the possibility of B-chromosomes may be mentioned these facts : none of the
S. x towneendii chromosomes stain differentially, neither do they differ greatly in size
(though this is by no means always a criterion as shown by Lima-de-Faria, 1948).Thirdly,
lagging or failure to pair at meiosis is not a common feature. Thus, except in 8.pectinata,
the evidence pointa not to B-chromosomesas the cause of chromosome number variation
but to aneusomaty.
Typically, there is variation around a chromosome number norm in S. a&emi$ora tiller
apices and in F1 hybrid pmc’s, and this agrees with aneusomaty. Aneusomaty is now
known in a number of plant genera, and striking instances are reported in Hymenocallis
Snoad (1966) and Chytonia, Lewis (1962). Aneusomaty also seems a most likely explanation since it is quite common in hybrids, apparently as a result of their genomic imbalance
(Klingstedt, 1939). In most of these cases the respective parental species are free of the
phenomenon, for example Triticinae amphidiploids (Sachs, 1962) and Gossypium (Menzel
& Brown, 1962).
Caution is always needed in ascertaining the existence of aneusomaty. Any somatic
chromosome counting technique is liable to damage cells. The broken cell walls cannot
always be detected and if chromosomes ere lost there is apparent aneusomaty. After
careful study, I am confident that the variations in chromosome numbers which I have
seen in my rSprtina preparations &rereal, and do not result from cell damage.
Despite the difllculties imposed by small chromosomes in Xpartinu there is fairly convincing evidence for aneusomaty. Its confinement to tillers in 8. alterni$ora and absence
from roots must be under some oontrol; presumably the extra chromosomesare subject to
elimination in root tissue but retained in the ‘germ-track’, perhaps in the same way as
Darlington & Thomas (1941) observed in #orghum, and Muntzing (1948) end Bmnziger
(1962) reported in Poa and Agropyron, respectively. Even in the tillers of 8.alterni$ora it
is clear from the small range of chromosome numbers (61-66) that selection is operating,
probably again by elimination of the more widely deviating and numerically unbalanced
cells. Although normal metephases contain 2n=62, it is possible that those pmc’s with
highly irregular meiosis may be aneusomatic, their unbalance leading to a breakdown of
gene control. This could explain why in 8. alternifira two adjacent anthers or even two
adjacent pmc’s can have regular and irregular meioses.
8.alterniflora reaently imported from America was not aneusomatic (Marchant, 1968).
Possibly the Southampton Water clone is so very isolated that inbreeding has led to
genetic disruption and aneusomaty.
The aneueomaty is developed to different degrees in different genotypes. In8. alterni@ra
it is apparently confined to somatic tiller tissue, but in the hybrids it also occurs in the
Evolution in Spartina (aruminme)I I
399
pmc’s. In both cases variation must result from preceding mitotic errors, which were seen
in S. alterniJlora and the hybrids (Plate 1, figs 3 and 0). These errors in non-pretreated
tissues are similar to the spontaneous mitotic abnormalities described in Lilium (Kato,
1955), and Solanum (Fukumoto, 1962) and appear to be the result of a breakdown of gene
control of normal divisions. This is perhaps correlated with poor environmental conditions.
Another possible cause is the ageing of clones and seeds, which has been suggested as
causing chromosome division breakdown (Peto, 1933 ;D’Amato, 1954 ;and Jones, 1962).
In the Spartina hybrids, in contrast to S . alterniJlwa, numbers must be perpetuated in
the tillers right through their development so that they are included in the pmc’s. The
reason for this difference from S. alterniJlora may lie in the special conditions created in
pre-meiotic divisions. In these transitional mitoses it has been shown by Oksala (1944)
that the precocity of meiosis begins to develop and causes instability in which mitotic
errors become more frequent, and this could be especially critical in a hybrid genotype such
as that of Spurtinu.
The parallel origin of aneusomaty in S. alternijoru and the hybrid Spartinas is of great
interest. It can be interpreted in terms of the parental role of S. alterniJlora, the latter
contributing the aneusomatic characteristics to the F1 hybrid. In the hybrid the pmc
variation does not apparently have the drastic meiotic breakdown effect seen in S. alterniJlora itself, perhaps because of genetic dilution by genes from the other, stable, S. maritima
parent.
In the Amphidiploid, where gene balance has been largely restored by doubling, the
range of aneusomatic variation is much reduced and different chromosome numbers
(120,122,and c. 124) in wild plants are evidence that aneusomatic gametes are functional
and result in chromosome races. In these Amphidiploids any small number variation is
buffered by the high ploidy level (122) and it seems that, being perennial, they can tolerate
chromosomal diversity and the slight instability and reduction of fertility which results.
Aneusomaty may represent an immature and unstable phase in the evolution of a genus
or species. In sexually reproducing plants, the products of fertilization by aneusomatic
gametes would mostly be too unstable to have survival value or any long-term evolutionary
advantage, but on a short-term basis some of the resulting progeny diversity could play a
special role in the rapid colonization of new habitats. Thus, although the chromosome
number variability increases sterility through mechanical disturbance at meiosis, it may
be of considerable adaptive advantage to S. x townsendii colonizing by seed over large
areas with numerous local variations in the habitat. Chromosome number variability can
therefore be regarded as an important initial phase in Spartinu evolution contributing to
the enormous evolutionary and ecological success of S. x tmmendii agg.
3 . Breeding systems, hybridity and genome relatiomhips
The most likely parents ofS. x t m e n d i i are S. maritima and 8.alterniflora on evidence
of circumstances, morphology and chromosome number. These two putative parents
seldom reproduce sexually in Britain. Indeed, ‘British’ S. alterniJlora always fails to set
seed. This is not a recent development,since Bromfield (1836)observed that Southampton
S.alterniJlora‘seldomperfects its fruit ’ and ‘perhapsneither this nor S.strictu (S.maritima)
mature seed abundantly anywhere in the wild state ’. S. maritima is the more fertile of the
two in this country with highly stainable pollen and occasionally a low percentage of
ripe seed or partially developed caryopses. This very poor seed fertility creates a paradox
in two species regarded as parents of a vigorous hybrid.
S. alterniJlora in Britain also has only partial pollen fertility. Meiotic disturbances
(a number of univalent8in quitea large proportion of pmc’s)are probably partly responsible
and this suggests that these clones are not representative ofthe species as a whole. Indeed,
recently imported seed samples of the species in Massachusetts, U.S.A. are highly viable
c. J. M . & R m T
400
and meiosis is regular in the few resulting progeny examined. More comprehensivestudies
are needed of meiosis and fertility in American clones of 8.alterni$ora.
In nature 8.maritima and S . alternifira both reproduce vegetatively by rhizomes and
tillers, thus avoiding sexual reproduction. S. alterni$ora may well be a single genotype in
the stands now remaining at Marchwood near Southampton and this, in a species adapted
to cross-fertilization,may automatically result in self sterility. Self-sterilityis also possible
in S. m r i t i m since experimentalcrosses of plants from separate localities yield more seed
S. al(erni$ora (6x+2)
5. marilima (62)
A A
B1
Bi Bp, Ba
1
/
9.x townacndii (c. 62)
Fi
A-A
Backcross (c.9~)
S42
A-A
I
A
10 111’s
(6observed)
homology
(rare
111’s.
univalents
univalenta C
Amphidiploid (c. 122)
gametee
A
Backcross (c. 72)
S31F
IV or
III+I
A-A
A
/
plus the equivalent of
14 genomes at random
from either parent
(i.e. from A, B and C)
Text-fig. 8. Genome relationships in the ‘8x tozvneencEii complex’.
1
Evolution in Spartina (Graminem)11
401
than crosses within one population. This species grows mainly in isolated colonies and
opportunities for fertilization between different genotypes may rarely occur. I n the past
the existence of a barrier to selfing in these two species may have increased the chances of
successful hybridization between them by eliminating the usual competition between
foreign and compatible (self) pollen (Lewis, 1947) which normally operates against
hybridization. It is true that attempts to cross them in cultivation were unsuccessful, but
no comparable tests were made on naturally growing plants in the field.
Owing to the polyploidy in the parent species genome analysis is complicated and there
are dangers inherent in making the initial assumptions of parental genome structure.
Nevertheless, Text-fig. 6 shows the possible genome formulae for each species and hybrid
in the Southampton Water complex using basic chromosome numbers, meiotic behaviour
(Table 9) and fertility. Alternatives would modify the detail but not the general pattern of
this analysis.
The relatively high maximum of pairing attained in the F1 hybrids (up to 20 bivalents
per pmc and up to 6 111+ 1 IV in multivalents per pmc) seems to indicate considerable, a t
least partial, homology between most genomes of S. muritima and S. alterni$ora. Interchanges in s.alternijora, already suggested as partly responsible for multivalents, may
be the cause of intergenome homology which is not given full expression in pairing because
chiasma frequency is too low.
Rod bivalents and heteromorphy in F1 hybrid pmc’s suggest that homology is not
complete, i.e. pairing occurs between the B, B1 and B2 sets. Loosely associated univalent8
in the cytoplasm also suggest that there is some residual homology. By contrast, a maximum of nine bivalents indicates closer homology between two parental genomes (A-A).
Pairing in the Amphidiploid is relatively straightforward, with chromosome doubling
restoring pairs of completely homologous genomes so that association occurs preferentially
between these homologues and is mainly bivalent-forming within parental chromosome
sets (autosyndesis). Quadrivalents are possible in the parental A-A sets (allosyndesis) of
the amphidiploid as also are bivalents and multivalents up to hexivalent level (inclone RB)
in the remaining B, B1 and B2 genomes (auto-allosyndesis).Sporadic secondary pairing of
up to three bivalents was seen, though rarely, in Amphidiploid pmc’s.
Text-fig. 6 also shows that the genome formulae of backcrosses 542 and S31P, though
impossible to predict with certainty, can be fitted into the scheme and related to meiotic
behaviour.
We may conclude that the amphidiploid origin of S. x townsendii agg. from S . maritimu
and S. alternijora, on similar lines to that of Aesculw curneu (Upcott, 1936)) can be
supported by genome affinities.The explanation is not without shortcomings and problems,
however. I n the first place, the widely differing parental chromosome numbers of 2n = 68
and 70 suggested by Huskins (1931) gave a more precise summation in 2n= 126 than do
the new numbers (60 + 62) in 2n = 120-124. Secondly, with the new numbers, there is now
a remote possibility of an autotetraploid origin of S. x townsendii from one of the two
diploids in Britain. However the low multivalent frequency in meiosis of S. x townsendii
Amphidiploid is slight, though not necessarily conclusive, evidence against autotetraploidy. Both S. alternijora and S . muritimu form mostly ring bivalents so that a n autotetraploid from them should have a relatively high multivalent frequency, but on the other
hand genetic control of chiasma frequency can occur in plants (Rees, 1961 ; Roseweir &
Rees, 1962) and this could reduce multivalent frequency in S. x townsendii. Taken
together, the evidence from the different biological and historical sources suggest amphidiploidy as the logical origin for S. x townsendii.
It is not clear whether S. alternijora a t Marchwood persists unchanged from the
American introduction of c. 1800 or is, as its variable fertility and meiotic irregularities
suggest, an inbred or even hybrid derivative of now-extinct S. alternijora which once grew
in the area. Clearly, no cytological evidence has been found against the hybrid origin of
S. x townsendii and the evidence supporting it is not conclusive ;no one has yet succeeded
c/ Present.
* Aneuaomatic.
76
531F (nearHythe)
124’
c.90
c.
120-127*
51-69*
62
60
542 (nearHythe)
Backcrosses
(Hayling I. and 1.o.W.)
S. alternijeora
S9a (Marchwood)
S. x taaneerulii F1
844 (Hythe)
S. x %owmendii
Amphidiploid
L1 and T6
(Lymington and Eling)
T10 (Essex)
s.maritima
Plant and locality
Chromosome
no. 2n
8-5
2-1 6
11-8
4-19
7.0
24-6
35.9
43-5
16.4
4.9
28.8
3.5
27.6
9-3
40-8
37-45
31.6
21-36
56-4
49-61
59.9
54-63
29.8
28-30
29.8
26-31
12.8
Total
2.0
0-8
2-2
0-8
23.4
26.3
Ring
6-19
6-4
4.5
Rod
2.2
0-12
32.2
2147
0-4
0-30
I
P
11
Mean metaphaee pairing per cell
Mean chia5nata
IV
0.94
1v
3 I11
16
20
0.88
0.86
0-74
0.65
2 IV
51v
+1
2IIIor
1N
5III
0.89
0.92
-
percell
P’
prd.
cbrom.
Max.
multivs.
61.2
77.4
104.2
87.9
18-1
54.2
55.2
per
Pmc
7
30
70
37
7
-
( %)
with
mults.
cells
Table 9. Summurized meiotic a d y s i s of the ‘S.x townsendii complex’
4
a
J . Linn. SOC.(Bot.) Vol. 60 No. 383
C . J. MARCHAST
Plate I
(Pcccing p . 402)
J . Linn. SOC.(Bot.) Vol. 80 No. 383
C.
J. MARCHANT
Plate 2
J . Linn. Soc. (Bot.) Vol. 60 No. 383
C. J. MARCHANT
Plate 3
Evolution in Spartina (Gramineae)
II
403
in crossing ‘British’ or American S. alterniflora with 8.muritima nor obtained an amphidiploid by chromosome doubling, yet this is claimed to have occurred in nature. Investigations in Britain may already be too late to prove the hybridization conclusively since one
of the speciesis represented by only two degenerating populations whose meiotic behaviour
and fertility is often abnormal. The solution to the problem may be found by investigation
of S. alternijlora in American habitats where it is endemic. Only then can we judge the
status of ‘British’ S. alternijlora and its possible parentage of S. x townsendii.
The remarkable success of S. x townsendii agg. (Marchant, 1967) poses the question of
why population explosions of new species are not seen more frequently in nature. The
answer may lie in the special conditions required; the initial advantage of S. x townsendii
F1 was due, not so much to any fortuitous fitness of its genotype for the available environment, though this was an important prerequisite, but to the vast area of uncolonized
habitat where competition was a t a minimum.
I n many areas including Southampton Water 8.x townsendii agg. has now completely
meadowed. The second and more complex evolutionary phase will be the natural selection
of the F1 hybrid and the chromosome races of the Amphidiploids where they compete.
Recently, Ford (1964) has described very striking cases of the genetic fluctuations in
natural populations of various insects and plants, and future changes in the Spartina
swards could be as spectacular. The dynamic situation in the S. x t m e n d i i agg. populations would repay continued study and add to our knowledge of speciation and ecological
genetics in plants.
ACKNOWLEDGEMENTS
I thank Dr G. R. Lane for supervising this work and Dr Keith Jones for encouragement,
criticism and advice during preparation of the manuscript. Much of the work was done a t
the Department of Botany, University of Southampton and supported by a D.S.I.R.
Research Studentship, for which I am grateful.
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EXPLANATION OF PLATES
PLATE
1
Mitotic chromosomes. Figs 3 to 7 phase contrast.
Fig. 1. Spartina ma*itima (521). Tiller apex mitosis. 2n=6O.
Fig. 2. Spartina altern$ora (S9a). Root tip mitosis. 2n= 62.
Fig. 3. Sprtina altemi$ma (SQa). Tiller apex mitosis. Dicentric bridge at telophase.
Fig. 4. Spartina x townaendii F1 hybrid (844). Tiller apex mitosis. 2n = 62.
Fig. 6. Spartina x lowttaendii Amphidiploid (L99). Tiller apex mitosis. 2n=c. 122.
Fig. (% Spartina x townaendik Amphidiploid. Tiller mitosis with anaphase laggards.
Fig. 7. Backcross hybrid (S31F). Tiller apex mitosis. 2n= 76.
Evolution in Sprtine (&aminme) I1
406
PLATE 2
Meiotic chromosomes.
Fig. 1. Spartina maritima (S21). Metaphese I. 30 bivalents and a persistent cytoplasmic nucleolus
(mowed).
Fig. 2. Spartina maritima (S21).Anaphase I. Note p-nucleolus (mowed).
Fig. 3. Spartina alterniflwa (S9a). Metaphese I. 30 bivalents+ 2 univalents.
Fig. 4. Spartina alterniflcwa (89s). Metephsee I. 31 bivalents, T w o (mowed)a m heteromorphic.
Fig. 6. Sprtina alterniflwa (S9b). Metapham I. 29 11+1 chain quadrivalent (mowed).
Fig. 6. Spartina aZterniJwa (S9b). Fragmentation at telophase I.
Fig. 7. Spartina x t m e n d i i Fi(S44). Metapham I. 1 N + 1 V + 4 I11+ 9 I1+ 20 I. 2n =69.
Fig. 8. Spartina x townaendii F1 (S44). Metaphese I. 2 I11+ 13 I1 26 I. 2n = 68.
+
PLATE 3
Meiotic chromosomes of S. x towneendii Amphidiploid.
Fig. 1. 63.1727. Anaphese I. 2n= 122.
Fig. 2. Clone RB. Metapheee I. 69 11+3 I. 2n= 121. Persistent cytoplasmic nucleolus -wed.
Fig. 3. Clone T10. Metaphase I. 60 11+1 I (mowed). 2n= 121.
Fig. 4. Clone L1. Anaphase I. 2n= 122.
Fig. 5. Clone L1. Metapham I. 1 IV+ 67 JI+ 1 I. 2n= 123. Some bivalents show seoondary pairing.
27