Bot. J. Linn. SOC., 66: 223-232. With 3 plates
April 1973
Variability in Prosopis farcata in Israel:
anatomical features of the seed
ELLA WERKER, A. DAFNI AND M. NEGBI
Department of Botany, The Hebrew University o f Jerusalem, Israel
Accepted f o r publication July 1972
Anatomical features of seeds of Prosopis farcara (Banks & Solander) Eig, collected at nine
localities from various geographical regions and habitats in Israel, were studied. The seeds differ
in size, shape and colour, and also in the cracking ability of the surface layer and whether the
palisade layer peels off from the rest of the testa upon imbibition or not.
The gum extruded during imbibition is formed in gum cavities extending from the
endosperm throughout the testa up to the palisades.
Water penetration is apparently barred by the outermost wall layers of the external cells of
the testa (palisade caps).
CONTENTS
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Introduction
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Materials and methods
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Observations
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Morphological features
Anatomical features . .
Discussion
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Permeability
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Gum and mucilage
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Differences between seeds collected at different localities
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Acknowledgements
References
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INTRODUCTION
This work is part of a broader study on the uniformity of the taxon Prosopis
farcata in Israel. Prosopis farcata (Banks & Solander) Eig (Mimosaceae) grows
in Israel in fields and on river banks and salines throughout the country. Seeds
of this plant collected at different localities differ in form, size and colour,
though those collected at each locality show considerable uniformity. In seeds
from some localities part of the seed coat is found to peel off after imbibition.
Seeds of Leguminosae share similar anatomical features. The structure of
their testa was reviewed by Netolitzky (1926) and Corner (1951), who defined
the following structures: 1. Cuticle. 2. A row of outer epidermal palisade cells,
each cell being composed of the following regions: a. mucilage stratum; b. an
outer rod-like stratum with a narrow lumen; c. an inner columnar stratum with
a wider nucleate lumen; d. Lima luckfa or light line, an optical line separating
223
224
E. WERKER, A. DAFNI AND M. NEGBI
(b) from (c). 3. Hypodermal hour-glass cells. 4. Mesophyll. 5. Inner epidermal
hour-glass cells.
Like many other Leguminous seeds, intact seeds of Prosopis spp. take a very
long time to germinate due to their impermeable seed coats (Crocker, 1909;
Nambiar, 1944;Barton, 1947;Khudairi, 1956;Meyer&Morton, 1971).
The common opinion held is that in the Leguminous seed the palisade layer
is responsible for the impermeability of the seed to water. Corner (1951)
attributes it mainly to the contraction of the palisade cells in general as the
seed ripens. Others specify a certain zone in these cells that acts as the barrier.
The following structures were the ones regarded by different authors as being
mainly responsible for impermeability: the cuticle (White, 1908; Rees, 1911;
Khudairi, 1956) or suberization of the outer periclinal wall (Hamly, 1932); the
zone of the light line, which is considered to have different physical and
sometimes chemical properties from the rest of the radial wall (Coe & Martin,
1920; Martin, 1922; Frey-Wyssling, 1959); pectic insoluble materials which
shrink upon desiccation and perhaps also undergo chemical changes that make
them less pervious to water (Raleigh, 1930). It should be remembered,
however, that the different opinions were deduced from research carried out on
different genera of the Leguminosae. Watson (1948), who examined the
anatomical structure of both hard and soft seeds of different genera, could not
find any specific characteristics of the hard seed coats which could be
responsible for their impermeability.
In the present study the anatomical features common to seeds of Prosopis
farcata from different habitats in Israel, and the characteristics of seeds of
different habitats, were investigated.
MATERIALS AND METHODS
Seeds of Prosopis farcata were collected from nine different habitats: 'En
Zin and 'En 'Aqrabbim ('Arava valley), Sedom and Kalia (Dead Sea area), 'Uja
(Central Jordan valley), Mahanayim (Upper Jordan valley), HaEla valley
(Judaean foot hills), 'Ein Baydan (Samarian hills) and Akhziv (northern coastal
plain).
Mature dry seeds were hand-sectioned. Mechanically scarified seeds were
soaked in Petri dishes at room temperature. The swollen seeds were sectioned,
longitudinally or tangentially, by hand or by a sliding microtome. The sections
were stained with the following stains: Reactif Genevois-for general differentiation, Sudan IV-for cuticle, phloroglucinol-for lignin, chlor-zinc-iodide
(ClZnl)-for cellulose, ruthenium red or hydroxylamine-ferric chloride-for
pectic substances (Reeve, 1959) and periodic acid-schiff reaction (PAS)-for
insoluble polysaccharides. An additional test for pectic substances and
hemicelluloses was made by extraction with 0.5% ammonium oxalate and 4%
NaCI respectively (Jensen, 1962). Carmine acetate was used for nuclei staining.
Pieces of seed coats were macerated in 0.5% chromic acid for at least 24 h. The
sections were examined under light, polarizing and phase-contrast microscopes.
For examination of vitality of the seed coat cells, thick sections of seeds at
different stages of swelling were put into solution of 0.5% 2 : 3 : 5-triphenyltetrazolium-chloride for 24 h (Fahn & Arnon, 1963).
Young seeds at various stages of development from a few localities were
PROSOP/S FAR CA TA SEEDS IN ISRAEL
225
fixed in FAA, em bedded in paraffin and stained with safranin-fast green (the
usual procedure being modified by dipping the sections in safranin for a few
seconds only).
OBSERVATIONS
Morph ological features
Seeds from all localities have the form of a flattened ovoid. The basic colour
is brown, the shade differing in seeds from different localities. The average size
of the seeds from each locality and their colour are given in Table 1.
Table 1. Size in mm + S.E. and colour of seeds of the different localities
Area
-.-....'Arava
Dead Sea
Jordan valley
J udaean hills
Samarian hills
Coastal plain
1
Locality
'En Zin
' En 'Aqrabbim
Sed om
Kalia
'Uja
Mahanayim
HaEla valley
' Ein Baydan
Akh ziv
Thickness
2.91
3.26
3.02
3.37
3.14
2.7 3
2 .9 1
3.25
3.01
± 0.10
± 0 .22
± 0.24
0.35
± 0.24
± 0.26
± 0 .62
± 0.22
± 0.30
±
Width
5.56 ± 0.20
5.41 ±0.26
6.15 ± 0 .32
4.99 ± 0 .10
5.84 ± 0.58
5.46 ± 0.26
5.03 ± 0 .68
5.27 ± 0.37
5.72 ± 0.47
Length
7.44 ±
6 .74 ±
7.64 ±
6.00 ±
7 .28 +
7 .49 +
5.94 ±
6 .45 ±
6.89 ±
0 .26
0.37
0 .54
0 .37
0.45
0.47
0.72
0.70
0 .57
Colour 1
2.5 YR 3/3
2.5 YR 3/ 3
7 R 3/4
10 R 3/4
5 YR 3/6
5 YR 3/6
2.5 YR 3/4
10 YR 4 / 6
5 YR 3/3
According to the classification of Mansell (1954).
No correlation is evident between geographical distribution, shape and size
of seeds. In all cases where seeds from more than one locality have been
sampled in a given geographical region, a uniformity of the seed colour or a
close similarity has been found.
Seeds from all localities have a horseshoe-shaped groove on each side, typical
of many Mimosaceae. This structure has been termed a pleurogram (Corner,
1951).
The seeds of P. farcata ripen in August-September. The surface of seeds
collected in 'En 'Aqrabbim, 'En Zin, Sedom and Kalia two months after
maturation was found to be cracked like dried earth crust. The seeds collected
at the other localities were smooth or had several longitudinal cracks
(Plate lA-C). However, when examined six months after maturation, seeds
from Akhziv and HaEla valley were also found to be ·cracked all over.
Anatomical features
Cuticle
A very thin cuticle covers the palisade layer.
Palisade cells
As seen from above (Plate lB), the surface of the mature seed consists of a
mosaic of concave pentagons and hexagons, varying slightly in shape and size.
Each polygon represents the outer layer of the outer wall of a palisade cell. It
226
E. WERKER, A. DAFNI AND M. NEGBI
appears to consist of concentric rings. In cross section of the seed coat
(Plate 2E-G) the palisade cells are elongated and very compactly arranged with
no intercellular spaces between them. The position of the light line changes
gradually according to the location of the cell on the seed (Plate 2E,F,H), being
approximately at the middle of the cell or slightly closer to its inner edge in the
centrally located palisade cells and closer to the outer edge (up to a distance of
about 4/5 of its height) in the seed margins.
The mature palisade cell can be regarded as consisting of three parts:
a. The main body of the cell. This consists of the radial and inner tangential
cell walls, which surround the lumen except its outer side. The cell lumen
approximately up to the light line has the shape of an hour-glass or is elongated
except for a widened base. Above the light line the lumen becomes very narrow
in the middle and extensively branched (Plate 2G,H).
According to their staining, in the main body of the palisade cell the walls
are composed mostly of cellulose. Only the outer part of the inner tangential
wall is composed of pectic substances. As seen with the polarizing microscope
and in maceration, the cellulose microfibrils of the radial walls run parallel to
the cell length. At the light line, however, the direction of the microfibrils
seems to be tangential (cf. Cavazza (1950) for Gleditschia).
b. Conical-shaped part of the outer wall of the cell (Plate 2E,F,H,I). Staining
shows that it contains both cellulose and pectins. The cellulose microfibrils in
this part are parallel to the cone surface.
c. The outer portion of the outer cell wall. This is situated like a cap on the
conical part of the cell wall and is composed of several superimposed
pectinaceous layers (Plate 2H), giving the appearance of concentric rings
observed in surface view.
In Prosopis, as in Cercidium (Scott et al., 1962), radial striation was observed
in the inner layer of the caps of the palisade cells, probably representing
passages for plasmodesmata.
The cap is stained by both ruthenium red and PAS but is not stained by
ClZnl. There are differences in staining of different portions of the cap.
However, it is very difficult to interpret these differences, as neither ruthenium
red nor PAS is specific. In an attempt to extract this part of the cell wall by
0.5% ammonium oxalate and by 4% NaOH, no sharp limit could be drawn
between portions extracted by either solutions. However, it was found that the
outermost part of the tangential walls is dissolved by ammonium oxalate,
indicating the occurrence of pectins, while most of the cap is dissolved only by
NaOH, indicating the occurrence of hemicelluloses. The conical part of the cell
wall .also completely loses its solid structure in NaOH, and only the cellulose
remams.
The manner of development of the palisade cells from cubical outer
epidermal cells of the integument is shown in Plate 2A-D.
In the seeds in which the palisade layer peels off while germinating, the
cellulose radial walls of the palisade cells were capable of considerable swelling.
The palisade cells of the other seed types have the same capacity to swell, as
can be observed in macerated tissue. The conical parts of the cell wall and the
caps, on the other hand, have a very low capacity to swell (Plate 21). As a
result, the palisade layer in the latter seeds tends to curve outwards.
PROSOPJS FARCATA SEEDS IN ISRAEL
227
The palisade cells contain coloured substances, the shade of which differs in
the different types of seeds. It is darker in seeds collected at 'En 'Aqrabbim,
'En Zin, Kalia and Sedam, and lighter in all the others. In addition, in all types
of seeds, there are cells rich in darker substances scattered among the other
palisade cells (Plates 1D, 2F,G). The density and manner of scattering of these
cells varies in the different types of seeds. They are most numerous, and appear
singly or in clusters of up to six cells, in the seeds from Mahanayim and are
most scarce, appearing singly, in those from HaEla valley and 'Ein Baydan.
The cracks observed on the surface of seeds growing in arid parts of the
country are usually not deeper than the region of contact between the palisade
caps.
Hypodermis and sclerij!ed parenchyma layer*
The sclerified parenchyma cell tissue constitutes most of the seed coat of
Prosopis (Plates 2F, 3A). In the middle of the seed in all seed types examined
this consists of about 25 rows (cf. Khudairi, 1956). The number of rows
increases along the vascular bundle in the seed margins. The SPC have thick
unlignified walls with numerous pits. In the swollen seed the cells are ellipsoid
with intercellular spaces between them. In the dry seed the cells are shrunken.
They are filled with coloured substances which are dark in shade in the seeds
from Sedom, 'En 'Aqrabbim, 'En Zin and Kalia, and are absent or light in shade
in those of Akhziv, HaEla valley, 'Ein Baydan, 'Uja and Mahanayim.
The cells of the outermost and innermost layers of the SPC are smaller than
those in the middle. Many of the cells of the outermost layer are
pumpkin-shaped (Plate 3A), a shape they acquire at a time close to seed
maturation. The number of these cells appear to be different in the different
types of seeds. They seem to be most abundant in the seeds from Akhziv and
scarcest in those from 'En 'Aqrabbim.
No inner hour-glass cells have been found.
A row of tangentially elongated cells is found on the inside of the SPC
layer. The cells are completely shrunken in the mature dry seed. On the inside
of this layer there is a row of big rectangular cells, the walls of which straighten
with imbibition. The outermost layer of the outer wall of the latter cells is
stained by Sudan IV and appears to be a cuticle. The intercellular substance
between these cells, and some regions on the outer layer of their inner
tangential walls is also stained slightly by this stain. This row constitutes the
remains of the inner integument.
Endosperm
Although endospermic structures in leguminous seeds were. d~scribed by
Nadelmann in 1889, new phenomena were found here. Early m 1ts development parts of the endosperm of P. [arcata disintegrate and turn i~1to. gum
(Plate 3D). Other parts remain cellular and the walls become mucllagmous
(Plate 3B). The endosperm of P. julijlora has been chemically analysed and was
found to be hemicellulose composed of galactose, arabinose and glucuronic
acid (Anderson & Sands, 1926; White, 1946; Anderson, 1949).
• Since the seed coat is not homologous with a leaf, we suggest calling Corner's (1951) mesophyll
scleri[ied parenchyma cells (SPC), a term describing their shape.
228
E. WERKER, A. DAFNI AND M. NEGBI
Gum cavities
As mentioned above, parts of the endosperm become mucilaginous through
disintegration of its cells (Plate 3D). This disintegration extends from the
endosperm through all the tissues of the seed coat, including the outer
epidermis (Plate 3C, E-G), thus forming gum cavities. Along its middle the
cavity is filled with gum (Plate 3E-G), while on the sides very thin-walled
mucilaginous cells and cells with ordinary walls but filled with mucilage can be
distinguished.
This lysigenous formation of the gum cavities starts early in the development
of the seed (Plate 3C). While maturing, the growing palisade cells close the
outer openings of these sacs with their thick outer walls. The mucilaginous
substance stains both with ruthenium red and Sudan IV, suggesting that it
contains both polysaccharides and terpene substances (Werker & Fahn, 1968).
The manner of its formation and its chemical composition enable us to refer to
it as gum. When the gum absorbs water it is capable of tremendous swelling.
The manner of swelling in the different types of seeds
When seeds from 'En 'Aqrabbim, 'En Zin, Sedam and Kalia imbibe water
and swell, the palisade layer becomes detached from the SPC tissue and peels
off. The detachment occurs between the adjoining walls of these adjacent
layers (Plate 3A). This phenomenon seldom occurs in seeds from Akhziv, HaEla
valley, 'Ein Baydan, 'Uja and Mahanayim. The detachment may be the result of
an enzymatic process starting upon absorption of water, or it may be a purely
physical process. In the latter case this may result either from dissolution of the
intercellular substance, or from intercellular substance connections between the
cell walls that are too weak to hold against the pressure exerted from within.
In order to clarify this problem the viabiliry of the seed coat of germinating
seeds from 'En 'Aqrabbim and 'Uja has been tested. This was done by
immersing portions of seeds at different stages of swelling in 2 : 3 : 5 triphenyl
tetrazolium-chloride. After 24 h only the embryo and the endosperm cells were
stained while the cells of the seed coat were not. Since it is unlikely that an
enzyme excreted by the embryo or endosperm penetrates through the SPC and
dissolves the middle lamella between the palisades and the subtended layer, it is
suggested that no enzymatic process occurs in the mature seed coat while
imbibing water.
In those seeds in which, after imbibition of water, the palisade layer does not
peel off, drops of mucilage are extruded from the secretory sacs upon the seed
surface. In those seeds in which the palisade layer does peel off the mucilage
spreads upon the SPC (Plate 3A).
Impermeability of the seeds
Experiments were made to localize the exact layer of the seed coat that is
responsibile for the seed's impermeability to water. Seeds were filed or
punctured to different depths. If they did not swell as a result of this treatment
a second deeper wound was made. After their swelling the seeds were sectioned
at the zone of the wounds in order to measure their depths. The seeds that
were only superficially scratched, i.e. had their cuticle and part of the caps
removed, did not swell. Seeds which were wounded more deeply reacted in
PROSOPIS FARCATA SEEDS IN ISRAEL
229
various ways: some of those that had been wounded to half the depth of the
palisade cells swelled on the following day while others, wounded as far as the
SPC, swelled only after eight days.
DISCUSSION
Permeability
In seeds from all localities examined the cuticle covering the seed coat is very
thin and it is cracked in the mature seed. After large areas of cu tide have been
scraped, water still does not penetrate into the seed. It is therefore not the
cuticle which causes impermeability of the seed coat. It seems to us that the
first and most important barrier for water entrance into the seed is formed by
the caps of the palisade cells. They are composed of substances which react in
the outer layer as pectic material and in the inner layers as hemicelluloses. We
could not find a clear cut distinction between the two types of substances. The
material of the caps probably becomes very compact when the seed dries. Its
swelling capacity when wetted is small and it probably prevents, together with
the very compact arrangement of the palisade cells, the entrance of water into
the seed. This hypothesis agrees with Raleigh's (1930) suggestion that shrinkage
of insoluble pectic substances of the outer portion of the palisade cells in seeds
of Gymnocladus (Caesalpiniaceae), upon desiccation, is responsible for the
impermeable condition. It also explains the findings of Kuehn (1925) and
Esdorn (193 O) that artificial drying or seasonal fluctuations in humidity
influence the number of hard seeds.
As a result of desiccation other parts of the palisade cells and other tissues of
the seed coat also shrink. Varying climatic conditions at the time of desiccation
may explain our results that different seeds need different minimal depths of
wounding for penetration of water.
It does not seem plausible to us that the zone of the light line is the main
zone where entrance of water is prevented, as suggested by Coe & Martin
(1920) and Frey-Wyssling (19 59). In germinating P. [arcata seeds from arid
regions, where the palisade cells are free to swell as they become detached from
the inner layer, swelling occurs also in the zone of the light line. From our
results, which are similar to those of Scott et a/. (1962) for Cercidium, it
appears that the light line is a region where the direction of microfibrils changes
from longitudinal to transverse.
Under natural conditions a slow process of cracking in the palisade layer
must occur, a process which is probably greatly accelerated by repeated rains
and/or changes in temperature. Thus, water uptake by seeds which are not
otherwise injured becomes possible with time.
Gum and mucilage
In Leguminosae, gum cavities often appear in vegetative organs (Tschirch,
1889; Metcalfe & Chalk, 19 50). In P. jarcata this typical feature of the family
was found in the seed. The gum extruded from the seed upon imbibition of
water comes from the gum cavities which extend throughout the whole seed
coat into the endosperm. Netolitzky (1926) mentioned the presence of resin in
230
E. WERKER, A. DAFNI AND M. NEGBI
seeds of Acacia spp. Tschirch (1889) mentioned the existence of slime spaces
("Schleimraume") in the seed coat of Theobroma cacao (Sterculiaceae).
In addition to the gum, which is capable of tremendous swelling, the cell
walls of the endosperm contain polysaccharide mucilage, also capable of
swelling greatly. Water cannot enter the dry intact seed. But when the seed is
injured, water enters through the wound and causes those tissues and materials
capable of swelling to do so, thus exerting a tremendous pressure on the outer
parts of the seed coat from within. In those seeds in which the palisade layer
does not peel off, this swelling causes the separation of the outer walls above
the outer endings of the gum cavities, and the gum is extruded as drops.
In view of the above results the term "mucilage-stratum" used for the outer
part of the palisade cell wall seems unsuitable, at least for P. !arcata. Our results
are in accordance with Chowdhury & Buth's (1970) observation that the seeds
of Cicer arietinum, although they have a "mucilage stratum", do not produce
any mucilage, while those of Cyamopsis tetragonolobus (both of the
Papilionaceae) produce a considerable amount of mucilage despite the absence
of a "mucilage stratum" on their palisade cells.
Those parts of the palisade cell walls which are mainly cellulose are capable
of swelling upon imbibition of water in a direction parallel to the seed's
surface. The differences in swelling capacity between the radial cellulose walls
and the very thick hemicellulose and pectic outer tangential wall of a palisade
cell causes this layer to curve outwards upon the extrusion of the radicle. It
straightens, however, if the surrounding tissue becomes dry again.
Differences between seeds collected at different localities
The different types of seeds differ in the following features: size, shape,
colour, cracking of the surface layer, peeling off of the palisade layer in the
swelling seed, the amount and manner of scattering of the more deeply
pigmented palisade cells and the structure of the layer inner to the palisade
layer.
Size and shape seem uncorrelated with ecological conditions. Small and big,
globular and flattened seeds, are found both in arid and moderate localities.
However, all the seeds collected in arid zones are darker in colour. The staining
substances are present both in the palisade and the sclerified parenchyma cells,
but since the lumen of the first and the portion of the seed coat which they
occupy are much smaller than those of the latter, the sclerified parenchyma
layer is the one which determines the seed colour. No correlation has been
found between the density of the darkly coloured palisade cells scattered in
this layer and the intensity of the seed shade.
In the seeds of the desert plants the capacity of the outer layer to crack is
much higher than that of seeds from more moderate localities. Since this also
occurred in seeds kept in the laboratory room, cracking cannot be attributed to
differences in climatic conditions between the different habitats. Most
probably it is caused by varying consistency of the intercellular substance
between the palisade cells.
The peeling off of the palisade cells seems to be the result of a process
occurring during the developing stages of the seed and not during its
germination.
PROSOPIS FARCATA SEEDS IN ISRAEL
231
Two main questions arise from the results obtained so far:
(a) whether the features typical to certain habitats have any adaptive value;
(b) whether these features are phenotypic, resulting from the conditions
prevailing in their habits, or genotypic. If the latter hypothesis is the
correct answer to the second question, then the species might not be so
uniform as has been thought hitherto. Since this research work is only part
of a broader study on the uniformity of the taxon P. /arcata, it is hoped
that these questions will be answered.
ACKNOWLEDGEMENTS
This investigation was partly supported by research grants from the General
Federation of Labour in Israel to E.W. and from the Central Research Fund of
the Hebrew University of Jerusalem to M.N. The interest and useful suggestions
given by Professors A. Fahn and C. C. Heyn are acknowledged.
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EXPLANATION OF PLATES
PLATE 1
Palisade cells of swollen seeds: A, a tangential section, surface view, as seen with phase
microscope ('Uja), x126; B, surface view of a whole mounted, peeled off layer; cracks can be
observed ('En 'Aqrabbim), x530; C, as B, x126; D, a peeled off layer mounted with the inner
side upwards; an optical section at a level where the lumen is wide; two darkly pigmented cells
can be observed (Scdom), x530.
PLATE 2
Longitudinal sections of the palisade layer of seeds at various stages of development (Kalia),
x424. A, cells short, thin-walled; 13, cells much elongated; initiation of thickening of the outer
tangential wall can be observed; C, outer layer of the cap formed; D, whole cap already formed;
initiation of formation of the conical-shaped part of the tangential wall can be observed; radial
walls arc still very thin; E, longitudinal section of the palisade layer of a mature seed, with
conical part of the outer wall conspicuous; the light line is at about 2/3 the height of the cell
('Uja), x424; F, longitudinal section of the seed coat; the light line is half way up the palisade
cells; three palisade cells with dark pigments can be observed (Mahanayim), x100. G, longitudinal section of the palisade layer at the centre of the seed; one cell with dark pigment can be
observed in the middle of the section ('En Zin), x424: H, partly macerated palisades; in the two
cells on the left the nucleus can be observed (Akhziv), x424; I, palisade layer peeled off a
swollen seed; caps of two cells removed as a result of squashing ('En 'Aqrabbim), x424.
PLATE 3
A, longitudinal section of sclerified parenchymatous layer of swollen seed, with palisade layer
peeled off; gum is spread on the outer surface ('En 'Aqrabbim), x320; B, longitudinal section of
endosperm of swollen seed, with mucilaginous cell walls ('En Zin), x320; C, longitudinal section
of very young seed, showing initiation of gum cavity formation (I) in a few palisades (Kalia),
x150; D-G, sections through a single gum cavity (G) in the endosperm and in different layers of
the seed coat (Kalia), x320; D, endosperm; the endosperm cells at the middle of the figure are
still thin-walled (cf. F); on the flanks of the figure and in the outer tissue bordering the
endosperm, disintegration has occurred and gum has formed; E, gum cavity in the middle of the
sclcrified parenchymatous layer; F, gum cavity in outer rows of sclerified parenchymatous
layer; G, outer end of gum cavity in the palisade layer.
Rot . ."f. Linn. Soc., 66 (1973)
E. WERKER, A. DAFNI & M. NEG BI
Pl ate 1
(Facing p. 232)
/Jot . ./. Linn. ,'-,'oc., (j6 (l 973)
E. WERKER, A. DAFNI & M. NEGBI
Pia
Bot ..'f. Linn. Soc., 66 (1973)
E. WERKER, A. DAFNI & M. NEGBI
Plate 3