Bat. J . Linn. Sac., 62, pp. 223-232. With 4 plates and 12 figures
April 1969
The development of the tuber in seedlings of five species of
Dioscorea from Nigeria
JUNE R. LAWTON, F.L.S.
AND
J. R. S . LAWTON
Department of Botany, University of Ibadan, Ibadan, Nigeria
Accepted far publication August 1968
Tubers in all five species develop from the hypocotyl region of the seedlings. A perivascular
cambium arises cutting off mainly starch-storing parenchyma and collateral vascular bundles
to the inside. A phellogen gives rise to cork on the outside. Between the two cambial layers
there may or may not be layers of parenchyma, not storing starch but containing raphides. The
vascular bundles consist of xylem with vessels, scalariform tracheids and parenchyma; and
phloem, with sieve tubes and parenchyma.
CONTENTS
.
Introduction
.
Materials and methods
Results
.
Discussion
.
References
.
Key to figure lettering
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223
224
224
229
230
231
INTRODUCTION
In continuing the study of the seedlings of Dioscorea species we hope to add to the
somewhat haphazard knowledge of the formation and structure of the tuber.
Descriptions of the tubers in the family Dioscoreaceae have been made over the
past century or more and some of these descriptions have included stages in the
development of the tuber. Burkill (1960) summarizes the available literature on the
subject and discusses the hypothetical evolution of the tuber from a rhizomatous
structure. It is a great pity that some of the references have been inadequately quoted.
I n the majority of reports the tuber is said to be a stem structure, although Goebel
(1905) describes the tuber as a root. According to Burkill both Decaisne and Duchartre
call the tuber of D. batatas Decne (probably D. opposita Thunb.) a root, although
Duchartre (1858) stated that he shared the opinion of M. Decaisne in seeing in the
tuber an analagous production to a rhizome, that is to say an underground stem, since
it arises from a special development of the caulicle portion of the embryo.
More recently, Martin & Ortiz (1963) described the tuberization of the American
species D. spiculijlora and D . joribunda and showed the tuber to be one or more lobes
224
J. R. LAWTON
AND J. R. S. LAWTON
of the hypocotyl. They conclude that the tubers represent much modified stem tissue
and thus are relics of an ancestral rhizome. The cambium is considered to be an
extension of the primary thickening meristem of the plumule apex and produces
storage parenchyma and conducting tissue on the inside and storied cork on the outside.
Ayensu (1966), in his description of the anatomy of the family Dioscoreaceae, states
that the structure of the mature tuber agrees more nearly with stem structures.
In this paper we have followed the further development of the five species investigated earlier (Lawton& Lawton, 1967), namely D.preussi; Pax (section Macrocarpaea),
D. bulbifera L. (section Opsophyton), D. hirtiJlora Benth. (section Asterotricha), D.
praehensilis Benth. (section Enantiophyllum) and D.odoratissima Pax (section Enantiophyllum).
MATERIALS AND METHODS
Seeds were germinated on damp filterpaper in a Petri dish in an incubator at 30°C.
When the radicle appeared through the testa the seedlings were transferred to damp
vermiculite in colourless, opaque, plastic boxes. The boxes were closed to conserve
moisture and placed in a light chamber having a 12-hour photoperiod. When the
first leaf had expanded the lids were removed. Seedlings were harvested at different
stages of development, then killed and fixed in FAA (formaldehyde-acetic acidethanol).
Drawings were made of each seedling before further treatment in order to relate
the sections to the external features. Before embedding in paraffin wax (m.p. SS'C),
the seedlings were trimmed, the shoots, leaves and roots were cut off to within a
few millimetres of the tuber and the remains of the seed removed; some of the longer
tubers were cut in pieces. Sections were cut at 10 p on a rotary microtome, fixed to
gelatine-subbed slides in formalin vapour, and stained in 1yo Bismarck brown.
Two-year-old tubers were available from D. praehensilis and D. bulbifera and sections
of these were cut on a freezing microtome in all planes. Small portions of these tubers
were also macerated in a mixture of chromic and nitric acids.
RESULTS
The results of the investigation are presented in the photographs and drawings that
follow.
It can be seen in the drawings (Fig. 2) that the tuber begins as a swelling at the
base of the plumule between the scales and does not appear to involve the primary
root in any way. It is not certain whether it can be said, therefore, to be part of the
hypocotyl since the absorptive cotyledon is at a different level from the emergent
cotyledon (Lawton & Lawton, 1967). I n any event it can be said that the tuber arises
from the upper part of the seedling, the caulicle region of Duchartre (1858) now called
the hypocotyl.
T h e first indication of tuberization is the formation of a cambial zone surrounding
the vascular tissue in the hypocotyl region of the seedling. I n some cases (Fig. 2E),
the cambial region seems to be continuous with the apical meristem of the first
TUBER
DEVELOPMENT
IN DIOSCOREA
225
plumular bud, The seedling of D.bulbifera (Fig. 1C) was very much younger than
the other seedlings, although the tuber was quite well developed. However, the
[1
cm
F
E
LL cm
FIGURE
1. A. Young seedling of D. preussii from which the longitudinal section shown in Fig.
2 A was cut.
B. Young seedling of D. praehensilis from which the longitudinal section in Fig. 2C was cut.
C. Young seedling of D. bulbifera from which the longitudinal section in Fig. 2E was cut.
D. Young seedling of D. odoratissima from which the longitudinal section in Fig. 2B was cut.
E. Young seedling of D. hirtiflora from which the longitudinal section in Fig. 2D was cut.
F. Older seedling of D. preussii showing the elongated tuber from which sections in Plates
IA,2 0 , 3A and 4A were cut.
cambium is only active in the tuber and does not give rise to any secondary tissues in
the stems of the seedlings studied. The cambium arises in the perivascular region
which, in the aerial stems, is frequently fibrous and forms a distinct separation between
the cortex and the central cylinder (Plate 2D).
J. R. LAWTON
AND J. R. S. LAWTON
226
The cambium gives rise to starch-storing tissue and vascular bundles on the inside
and it is not certain whether any tissues are cut off to the outside (Fig. 3, Plate 1D). As
FIGURE
2. A. Longitudinal
section through seedling of D. prmsii showing the beginnings
ofthe cambium (c) and the cork cambium (p) forming an apex to the tuber. A dormant bud (b)
is also shown.
B. Longitudinal section through seedling of D. odoratissirnu showing the meristematic (m)
region in the hypocotyl. This is a younger seedling than in A and the bud shown is the plum&
bud (pb) of which only the first leaf has come above ground.
Longitudinal section through seedling of D. praehensilis showing cambium (c) and cork
cambium (p).
D.Transverse section through seedling of D. hirtiflora showing two patches of cambium (c)
and two buds (b) in addition to the plumule, which has emerged.
E. Longitudinal section through seedling of D. bulbifera showing the cambium (c) right round
the hypocotyl region and continuous with the rneristematic cells of the plumule apex (pb).
c.
swelling proceeds a phellogen develops very close to the epidermis, cutting off corky
cells to the outside (Plate 2B). This cork cambium may remain quite separate from
the vascular cambium, even around the apex of an elongated tuber, though they may
merge (Plate 1 B). In some places it was difficultto distinguish between the two cambia,
TUBER
DEVELOPMENT
IN DIOSCOREA
227
so that there appeared to be cork tissue cut off to the outside of the meristematic
zone and storage and vascular tissue towards the inside. This merging of the two
cambia could be seen on the same sections showing two separate and distinct meristematic zones. After some time the vascular cambium ceased activity, although the
cork cambium remained active. Successive tangential cork cambia were produced
by the older tubers (Plate 3 B), sometimes so deeply seated as to be within the vascular
area; these successive cork cambia overlapped at several points to give the appearance
of storied cork, as shown by Esau (1960: 152). I n D. bulbifera the outermost layers
were lignified, not suberized (Plate ZC).
A transverse section through a young tuber (Plate 4A) shows the zonation clearly:
an outer cork zone, within this a clear cortical zone and a central storage zone with
vascular tissue. T h e cambium separates the cortical zone from the central storage
FIGURE
3. Camera lucida drawing of portion of hypocotyl of D.odoratissima showing cambial
zone (c) and the formation of new vascular bundle (v) from a single file of cells, and files of
starch-storing parenchyma (s). A cell containing raphides (R) can be seen to the outside of the
cambium.
zone. I n the mature tuber the cortical zone is still clearly defined but the central zone
has enlarged considerably. I n D . praehensilis the two zones are separated by a zone
of fibrous tissue in the mature tuber (Plate 1C).
Some tubers develop a highly meristematic apex but this depends on the species;
D. preussii is an example (Plate 1A). I n all the tubers investigated the development is
variable and maximum growth takes place in one area only, where the tuber elongates
and forms the normal lobed appearance, while the rest of the cambium contributes to
a slow increase in the diameter of the tuber. T h e vascular cambium thus may show
different rates of formation of new tissue in different areas at different times. I n
D. preussii, D. praehensilis and D . odoratissima the tubers are longer than they are
broad and have a distinct apical growth region, whereas in D. bulbifera the tuber
tends to be spherical and the entire cambium contributes to the formation of new
tissue at an equal rate. However, this species can produce lobed tubers so that at
some time there must be a variation in the rate of cambial activity.
The vascular tissue arising in the young tuber bears no relation to the root type of
organization at any point in its development, and differs slightly from the normal
seedling stem type as seen in the aerial stems. I n the aerial stems the vascular bundles
16
228
J. R. LAWTON
AND J. R. S. LAWTON
are collateral and may have from three to five phloem strands (Plate 2D). T h e bundles
are not scattered and tend to lie in a single layer, the smaller bundles interspersed with
the larger bundles, and very often surrounded by a layer of fibres or cells easily
distinguishable from the outer layers. The roots of the young plant have a typical
tri- or tetrarch structure, surrounded by a well-defined endodermis (Plate 3 C). T h e
bundles of the tuber anastomose irregularly throughout the tuber and are generally
collateral with a single phloem strand (Plate 3 D).
Near the edge of the vascular cylinder the storage cells are arranged in radial rows
interspersed with small bundles ; enlargement of the storage cells disrupts the radial
arrangement further in. The bundle is formed from a single file of cells of the cambium
which divide many times to give a group of small, highly nucleated, elongated cells
(Fig. 3). Further divisions give rise to the radially elongated collateral bundle (Plate
3 A) which may anastomose with other bundles. Divisions within the bundle continue
for a long time, even after the perivascular cambium has ceased activity. I n D.
praehensilis groups of fibres are also produced in this manner (Plate 1C). T h e region
outside the cambium consists of parenchyma cells which do not store starch, but many
of the cells contain raphides. Raphide cells may also occur within the starch-storing
region. In mature, second-year tubers the cambium was not clearly defined, but there
were still well-defined cork cambial layers. I n D.bulbifera some of the cortical cells
showed random divisions (Plate 2A).
Maceration and longitudinal sections of both mature and seedling tubers showed
the presence of vessels, tracheids and parenchyma in the xylem. The vessel elements
varied considerably in length and in type of thickening, showing annular, helical,
scalariform and reticulate thickenings, but in general the perforation plate was
oblique. Tracheids were more numerous, generally shorter than the vessel elements,
up to 0.2 mm long, with scalariform thickening (Plate 4B).
I n the phloem there were sieve tubes and parenchyma, the parenchyma being
short cells with very obvious nuclei. A study of the sieve tube elements showed two
types of sieve plate as described by Lawton (1966). The sieve tubes near the outer
edge of the bundle were narrow with transverse simple sieve plates and those nearer
the centre were wider with compound oblique sieve plates (Plate 4D, E). Thus we
have both juvenile and mature sieve tubes in the same bundle (Plate 4C), indicating
prolonged development activity within the phloem.
The tuber arises from one side of a very short hypocotyl region and the primary
root plays no part in its formation. However, the primary root plays a much greater
part in the life of the seedling than it does, for example, in the grasses. T h e tuber is
not always formed immediately the seedling is able to photosynthesize and may be
delayed for several weeks. The young seedlings must therefore depend on the roots
other than those of the tuber which play such a large part in the root system of the
mature plant. If grown in water culture, the primary root and its lateral branches form
the main root system of the plant. Adventitious roots arise from the hypocotyl and
epicotyl even before the tuber begins to form and the large number of roots complicates
a study of the anatomy of the tuber. These adventitious roots formed on the seedling
possessed three to eight protoxylem arcs, and were very deep-seated in origin from the
centre of one or more vascular bundles, between the xylem and phloem.
TUBER
DEVELOPMENT
IN DIOSCOREA
229
It has been noted that buds frequently arise on the seedling near the top, epicotyl
end of the tuber as it begins to develop. These tuber buds do not develop into new
shoots immediately but will do so if there is any check to the development of the
plumule.
Growth of a new stem from a mature tuber always takes place near the point of
attachment of the tuber to its parent stem, remote from the apex. Pieces of tuber
tissue show marked polarity in bud production, buds always being formed at or near
the morphologically upper end.
DISCUSSION
From the foregoing description of the tuber development it can be seen that the
tuber is quite clearly a development of the hypocotyl region of the seedling. T h e
compactness of the region makes it easy to understand why so many of the earlier
workers described the tuber as a development of the root, although the structure of
the two regions is quite distinct.
The enlargement of the hypocotyl region is due to the activity of an organized
layer of meristematic cells giving rise to distinct radial rows of parenchymatous
storage cells and collateral vascular bundles. Thus one can call the meristematic
layer a vascular cambium and it is similar in all ways to that reported in other members
of the Liliiflorae by Scott & Brebner (1893). T h e cambium thus arises in the hypocotyl
as in Dracaena (Cheadle, 1937), but in Dioscorea does not extend into the shoot or the
root and the continued activity of this cambium results in an outgrowth and swelling
of the hypocotyl region. I n the very young seedling the cambium might be regarded
as a continuation of the primary thickening meristem, but if this is the case the continuity is very brief. T h e region occupied by the cambium can be termed the pericycle
according to the definitions of Petersen (1892).
T h e shape of the tuber depends on the local persistence of the meristematic zone.
In spherical tubers, e.g. D. bulbifera, the meristem remains active over the whole
surface of the tuber until maturity, when the cambium ceases activity; in lobed and
elongated tubers the meristem becomes partially inactive and localized apical regions
of activity are formed. Elongated tubers such as D . preussii and D. praehensilis have
a well-defined apex; the cambial zone at some distance from the apex soon ceases
activity so that the width of the tuber is very uniform throughout its length. Burkill
(1960) suggests that tubers are the remains of an ancestral rhizome and this analogy
has also been suggested by Duchartre (1858) and Martin & Ortiz (1963). T h e idea
of a structure with an active apex at the end remote from the bud-producing region
seems to be at variance with a rhizome theory, unless the elongation of the tuber is
considered to be a more recent development. However, we do not propose to consider
here this hypothetical phylogeny of the tuber.
T h e apex of elongated tubers is interesting and we hope to study its organization
further. T h e whole apex appears to consist of a very deep homogeneous zone; thus
we cannot say whether the most active region is deep-seated or superficial. Bundles
seen in the tuber presumably originated from the apex and their further growth is
continued Ey the lateral cambium. I n structure all bundles were similar, being collateral with one phloem group and a few vessels and sieve tubes per bundle. T h e
230
J. R. LAWTON
AND J. R. S. LAWTON
vessels showed annular, helical, scalariform and reticulate types of thickening, though
presumably this thickening is related to the rate of growth of the tuber. The tracheids
invariably showed scalariform thickening which, according to Cheadle (1937), is
rarely found in secondary bundles. However, it is debatable whether the nomenclature
of ‘primary’ and ‘secondary’ related to the bundles is applicable in a description of
these organs.
The phloem of the bundles was extremely interesting in that both juvenile and
mature sieve plates were seen in the same bundle. \The disposition of these elements
showed a definite centripetal development and could be used as an indication of the
stage of differentiation of the phloem in the same way that the thickenings of the
vessel walls can be used to indicate the stage of xylem differentiation. Thus we could
call the part of the phloem nearest the outer edge, with narrow sieve tubes and simple
transverse sieve plates, the protophloem, if such a term can be applied to a bundle
formed from a cambium. Cheadle (1948) considers the sieve element with the simple
transverse sieve plate to be more specialized than those with the oblique compound
sieve plates. This was based on a study of a wide range of families in the Monocotyledoneae, including the Dioscoreaceae. However, there is no mention of finding both
types of sieve element in one bundle as we have here. Lawton (1966) figures the
transverse sieve plate from the stem apex, and such structures are also found in the
funicle. It is possible that in Dioscorea the elements with the transverse sieve plates
are produced in the most actively elongating region, but it may not be correct to say
that these are the most actively translocating regions, as was suggested by Cheadle
& Whitford (1941). This change in the type of sieve plate during the ontogeny of the
phloem is also the reverse of what one would expect if Cheadle’sview of the phylogeny
of the sieve tube is regarded as correct.
The whole bundle contains a large amount of meristematic cells and these are
gradually confined to the centre of the bundle. At this point divisions appear to be
mostly periclinal. Can this be a relic of an intrafascicular cambium such as that
reported by Chouard (1937) for Tamus, a close relative of Dioscorea ? This extension
of the development of the bundle changes the shape of the bundle in transectional
outline from circular to elongated oval.
Cork formation seems to be definitely from a phellogen layer and is not of the
storied cork type, as was stated by Martin & Ortiz (1963). There are definite layers
of meristematic cells and in appearance the cork layers Iook more like the ‘Initialenkork’ than the ‘Etagenkork’ (as described by Philipp, 1924). Although several layers
of cork are formed and at points where the layers overlap the appearance of storied
cork is seen, we do not think that this cork is normally of the storied type.
Thus in this investigation we agree on the whole with Martin & Ortiz (1963) that
the tuber is a development of the hypocotyl of the seedling and that the increase in
size is due to the development and further activity of a cambial zone in the perivascular
region.
REFERENCES
AYENSU,E. S., 1966. Vegetative anatomy and taxonomy of Dioscoreaceae. Ph.D. thesis, University of
London.
BURKILL,
I. H., 1960. The organography and evolution of Dioscoreaceae, the family of yams.J. Linn.
Soc. (Bot.),56: 319-412.
TUBER
DEVELOPMENT
IN DIOSCOREA
23 1
CHEADLE,
V. I., 1937. Secondary growth by means of a thickening ring in certain monocotyledons.
Bot. Gaz. 98: 535-555.
CHEADLE,
V. I. & WHITFORD,
N. B., 1941. Observations on the phloem i n the Monocotyledoneae. I.
The occurrence and phylogenetic specialisation in the structure of the sieve tubes in the metaphloem.
Am.9. Bot. 28: 623-627.
CHEADLE,
V. I., 1948. Observations on the phloem in the Monocotyledoneae. 11. Additional data on
the occurrence and phylogenetic specialisation in structure of the sieve tubes in the metaphloem.
Amy, Bot. 35: 129-131.
CHOUARD,
P., 1937. La nature et le r6le des formations dites ‘secondaires’ dans l’edification de la tige
des MonocotylCdones. Bull. SOC.
bot. Fv. 83: 819-836.
DUCHARTRE,
M., 1858. Dioscorea batatas Dcne.J. Soc. Imp. Centre Hort. 4: 465-478.
ESAU,K., 1960. Anatomy of seed plants. New York: John Wiley.
K. VON,1905. Die Knollen der Dioscoreen und die Wurzeltrage der Selaginellen. FZora,Jena,
GOEBEL,
95: 167-212.
LAWTON,
J. R. S., 1966. A note on callose distribution on the phloem of Dioscoreaceae. Z . Pflanzenphysiol. 55: 287-291.
LAWTON,
J. R. S. & LAWTON,
JUNE R., 1967. The morphology of the dormant embryo and young
seedling of five species of Dioscorea from Nigeria. Proc. Linn. Soc. Lond. 178: 153-159.
MARTIN,I?. W. & ORTIZ,S., 1963. Origin and anatomy of tubers of Dioscoreaflm*bundaand D. spiculiflora. Bot. Gaz. 124: 416-421.
PETERSEN,
0 . G., 1892. Bemaerkningen om den Monokotyledone Staengels Tykkelsevaext og anatomiske Regioner. Bot. Tidsskr. 18: 112-126.
PHILIPP,M., 1924. u b e r die verkorkten Abschlussgewebe der Monokotylen. Biblthca bot. 92: 1-28.
SCOTT,D. H. & BREBNER,
G., 1893. On the secondary tissues in certain monocotyledons. Ann. Bot. 7 :
21-62.
KEY T O FIGURE LETTERING
ar
b
C
e
ec
f
k
m
OSP
P
Pb
Ph
Pl
adventitious root
bud
cambium
endodermis
emergent cotyledon or first photosynthetic leaf
fibres
cork
meristematic cells
oblique sieve plate
phellogen, cork cambium
plumular bud
phloem
plumule
pitted vessel
raphide
primary root, radicle
starch-storing parenchyma
S
sk sclerotic cork layer
SP sieve plate
sieve tube
st
tracheid
t
tSP transverse sieve plate
vascular bundle, vascular tissue
V
xylem
X
xv xylem vessel
PV
R
ro
EXPLANATION OF PLATES
PLATE
1
A. Longitudinal section through apex of tuber of D. preussii shown in Fig. 1F.This shows the broad
meristematic zone (m) and the anastomosing vascular tissue (v) in the starch-storing tissue (s). x 40.
B. As in A, showing the organization of the apex with the most meristematic region to the inside of the
zone (m) and the outer covering of cork (k) formed from the outer layers of the meristematic region (p).
x 120.
C. Transverse section through mature, two-year-old tuber of D. praehensilis, showing cambial zone
(c) with new vascular bundles (v) in storage parenchyma with outer zone of fibrous tissue (f) and groups
of fibres. Also showing the cork layers (k) and phellogen (p). x 40.
D. Transverse section of seedling tuber of D. praehensilis, showing the cambial zone (c) giving rise to
vascular bundles (v), starch-storing parenchyma (s) and raphide cells (R). x 300.
PLATE2
A. Meristematic cortical cells from mature tuber of D. bulbifera. There was no organized cambium in
this tuber at this stage. x 480.
232
J. R. LAWTON
AND J. R. S. LAWTON
B. Transverse section through seedling tuber of D. praelaensilis in partially polarized light. T h e lignified
tissues in the bundles (v) show as white patches. In this section there are several bands of meristematic
cells (m) of which possibly the outer bands are cork forming (k) and the inner band giving the new
vascular tissue and starch-storing parenchyma (s). x 120.
C. Transverse section through mature tuber of D. bulbifera showing successive layers of cork (k) where
the tangential bands overlap. The outermost layer is of sclerotic cells (sk). x 480
D. Transverse section through young aerial stem of D. pveussii, showing the perivascular fibres (f)
and the vascular bundles with three phloem groups (ph) and two large xylem vessels (xv). x 120.
PLATE
3
A. Young vascular bundle from T.S. young tuber of D. preusSii, showing the nucleated phloem parenchema cells (ph), the large sieve tubes (st) near the centre of the bundle and the xylem tissue (x).
x 480.
B. Transverse section of mature bundle of D. bulbifera showing the successive tangential cork layers
(p), the outer sclerotic layers (sk) and the central starch-storing region (s). In this section no organized
vascular cambium could be seen. x 40.
C. Transverse section through primary root of D . pvaehensilis showing three phloem groups (ph) and
the well-marked endodermis (c). x 480.
D. Transverse section through mature tuber of D. praehensilis showing groups of fibres (f), raphide
cells (R) and a single vascuIar bundle with one large xylem vessel (XV)and a single group of phloem
cells (ph). x 120.
PLATE
4
A. Transverse section through tuber of seedling shown in Fig. l F , showing outer cork layers (k),
cortex with raphide cells (R), cambial zone (c) and central starch-storing region (s) with vascular
bundles (v). x 40.
B. Xylem elements from maceration of mature tuber of D. praehmdis, showing large pitted vessel
(pv), small scalariform tracheids (t) and part of a fibre (f). x 480.
C, D, E. Phloem elements from longitudinal section of tuber of D. praehensilis stained in buffered
aniline blue and illuminated with ultra-violet light.
C. Shows a large oblique compound sieve plate (osp) next to several small simple transverse sieve
plates (tsp). Thus we have both mature and juvenile sieve tubes in the same bundle. The cambium
was on the side of the transverse sieve plates. x 480.
D. Juvenile sieve tube with single, simple transverse sieve plate (tsp). x 480.
E. Complete sieve element showing oblique sieve plates (osp), one at each end. There are also several
juvenile sieve tubes with transverse sieve plates (tsp). The mature sieve elements show considerable
lateral wall pitting. x 168.
Uot. J. Ltm. Soc., 62 (1969)
J. R. LAW'I'ON
NU
J . It. S. LAWl'ON
Plate 1
(Facing p . 232)
Bot. J . Linn. Soc., 62 (1969)
J . I<. LAL4”I’ON
4ND
J . 11. S. LL4\V’I’ON
Plate 2
Uot. J. Linn. Soc., 62 (196Y)
J. R. LAW'TON
L NU
J . K . S. LAMi'l'Oru'
Plate 3
Uot. J. Livm Soc., 62 (1969)
l'latc 4