J . Linn. Soc. (Bot.),56, 367, p . 413
With 9 platea
Printed in &eat Britain
413
Growth, development, and effect of the environment on the
ultra-structure of plant surfaces"
BY BARRIE E. JUNIPER
The Botany School, University of Oxford
Communicated by DR W. G. TEMPLEMAN,
F.L.S.
It has been demonstrated in many species of plants that wax is extruded or migrates
on to the surfaces of the leaves and stems, both as a smooth layer and in a structural
form which results in a visible 'bloom' (Juniper, 1959). Where a bloom is formed the
carbon replica technique reveals under the electron microscope minute projections from
the cuticle surface of many different forms (Juniper & Bradley, 1958). The discovery of
these wax projections on plant surfaces immediately raises the problem of how such fine
structures develop and whether they may be modified by the environment. The size and
density of the wax projections found on leaves which are as small aa it is possible to
handle are practically identical with those on fully grown mature leaves. This seems to
indicate that wax formation takes place at a very early stage in leaf development. It
also seems to indicate that, because the density of the projections in the mature leaves
of most waxy species is only a little less than in the very young leaves, continuous production of wax during leaf expansion must be taking place. Because of the difficulty
of handling very small leaves in making carbon replicas, it would have proved very dificult to follow the formation of lcaf wax by taking replicas from successively smaller
leaf primordia. It was thought possible that the development of leaf wax, since folded
leaves have no visible bloom, is stimulated by light, and the following experiment was
planned to study the growth of leaf wax under artificial conditions, by totally depriving
the developing leaves of light a t an early stage.
Peas (Pisum sativum var. Alaska) were grown in sand in total darkness a t 18" C. for
8 days and were then transferred to a light intensity just below 5000 ft.-candles (approximately full summer daylight). Carbon replicas were immediately taken from the minutc
l a v e s which had already developed and succeasive replicas were taken from corrcsponding
leaves every 24 hr. The development of both the adaxial and abaxial leaf surfaces way
followed simultaneously, and the results of this are shown in Pls. 1-3.
Both the appearance (under the electron microscope) and the contact angle of the
surface of a pea leaf grown in darkness are very similar to those of dicotyledonous species,
which have no apparent surface wax projections (cf. Pls. la, 6 a and 7a).
PI. 1a shows the adaxial surface of a pea immediately after transfer from darkness to
light, and a t this point the adaxial surface is very similar to the abaxial, although they
become very different from one another later on. "he development of the wax on the
adaxial surface appears to begin immediately the plants are transferred to light. Twentyfour hours after transfer (see Pi. l a ) minute 'crystals' of wax, still disorganized in shape
and distribution begin to appear on the adaxial surface. The abaxial leaf surface, away
from the light, seems to lag behind in development a t this stage and the appearance
shown in P1.2d persists until about the third day. P1.1 c shows the stage of development
of the adaxial surface by the second day; the crystals are now clearly distinguishable
from the background and are beginning to assume a regular shape. In contrast t o the
The Council of the Society is much indebted to Imperial Chemical Industries, Ltd., for a
financial grant covering the estimetedcoet of making and reproducing plates illuetreting Dr Junipor's
Paper.
414
BARRIEE. JUNIPEIR
observations of Mueller, Cam & Loomis (1964), no pores or pita through which the wax
could have been extruded have ever been seen in the pea or in any other species with a waxy
bloom. Since the appearance of P1. 1b suggests very strongly that prior to the contact
with the atmosphere the wax is still in a liquid form, it seems unlikely that any surface
replica technique will reveal extrusion pores. Such pores, if present, would be below the
level of resolution of the light microscope and could only be resolved by some ingenious
form of counter-staining and ultra-thin-sectioning which would distinguish them from
the surrounding pectin and cutin layers. Pls. 1d and 2 a show, at different magnifications,
the appearance of thc adaxial surface after 3 days. The crystals have completely covered
the leaf surface with the exception of the guard celh around the stomata, but they are
n t i l l angular with more or less straight sides and have only reached about @6p, twothirds of their ultimate height.
On the fourth day after transfer, changes can be seen for the Grst time on the abaxial
surface. This is shown a t different magnifications in Pls. 3a and b. From this point
development on the lower side of the leaf proceeds very rapidly. Projections completely
cover the lower surface of the leaf by the end of the fourth day and by the fifth day
(compare P 1 . 3 with
~ 2 b and 2 c ) the abexial surface has drawn level in development with
the adaxial, although, as is clear from the micrographs, the final result is entirely different at the submicroscopic level, From the aeventh day after transfer (see P1. 3 4 no
further changes are observed in the fine structure of the leaf; the crystals on the edaxial
surf~ceno longer have the angular appearance of those in P1. l c ; those on the abaxial
surface have likewise lost the peglike appearance of P1. 3b and have developed into an
interlocking mesh.
It is, of course, only conjecture that the progress of the fine structure of the leaf Burface from the primordial to the mature leaf follows this pattern. But this is of some
importance for undersown crops or weeds growing under crops which are later harvested
may be faced with such a situation (a rapid transfer from low to high light conditions)
end it seems likely that the pattern of development illustrated above reaembles that
occurring under natural conditions.
One of the most remarkable featurea of the development of these surface waxes is
that growth is determinate. Therefore, analogies with such phenomena as 'myelin tubes'
(see Frey-Wyaaling, 1948), in which growth is both uncoordinated and continuous,
cannot be drawn. All the species with a wax bloom that I have examined appear to
have projections that, grow only to a critical length or size. The branched wax tubes of
Ghrysanthemum segetum (PI. 4 a ) extend to a maximum of about 2 p and then cease
growth. The tubes of this species appear to be smooth even under the highestmagnification, but several of the surfaces, particularly those shown in P1. 4b, c and d, would seem
to have projections showing a definite repeating pattern of growth. This pattern is particularly noticeable in the cabbage Brassica; o k r m var. q i t a t a (Pl. 4 b ) and the three
tubes just below and left of centre in this micrograph have a quite striking segmented
appearance. A small group of tubes a t a much higher magmflcation is shown in P1. 4 c .
The suggested interpretation of this surface is that small (0.26-0*Sp)and more or less
annular are4w in the cuticle of the young leaf begin to secrete wax on to the surface. Aa
the leaf ages and enlarges these secretory rings become larger, more areas of secretion are
formed and two or more of these rings may fuse together to give fasciated bundles of
projections. The upper left-hand edge of P1. 4 b is probably an example of the result of
such a fusion. The expansion of the areas of secretion would also explain why many of
the tubes appear to taper from the base (see PI. 4 c ) .The walh of these tubes are extremely
thin (this can be seen clearly in P 1 . 4 ~ )and the tubes themselves very delicate, 80 that,
even in plant8 grown in the constant temperature room, the majority of the tubes will
have broken off and will be lying on their sides.
Evidence from wiping the surface off cabbage leaves a t regular intervals indicates that
wax production continues until a very late stage in leaf expansion, so that the surface
Effect of environment 012 the ultra-structure of plant surfaces
415
of an old cabbage leaf is made up of a tangled mass of broken wax tubes with wax
production still continuing a t the base of the tubes. It is tempting t o suggest that the
rings that we see on these wax tubes (PI. 4c) represent some form of phasic growth, as
if the wax was not secreted in an even flow but with a more or less regular rhythm. What
the relationship is between these ' growth rings ' and the age of the wax tube itself is not
yet clear. Nor is i t clear why the projections of only a very few species have this repeated
pattern within each individual projection. It is quite clear, however, even from casual
observation, that extension in depth of the wax layer on brassicas does take place; the
greylwhite surface bloom of the young leaf is replaced, if aerial weathering is not too
severe, by the thick bluelgreen bloom of the old leaf. Growth of the projections does not
continue indefinitely but at what point in leaf expansion it ceases, if there is a definite
point, has not yet been determined. A restriction in growth can also be seen in those
species which secrete wax in the form of tufts. Pls. 5 a and b show good examples, and it
appears that whatever the age of the leaf and whatever the environmental conditions
these tufts grow to a certain diameter but never fuse t o give a uniform layer.
It seem that most plants of the temperate zone with waxy leaves, whether they are
of the individual crystal type such as the pea (Pisum sativurn) or a network of tubes,
such as Chrysanthemum segetum (Pl. 4 a ) , or a carpet of isolated tufts such as Papaver
somniferum (Pl. 5a) or Kkinia articulata (Pl. 5b) given a comparable environment seem
to reach a more or leas uniform depth and density of projections and persist. However,
there is some evidence that the iine structures on contiguous epidermal cells, or over the
surface of a single cell may at any one time be at different levels of development. This is
demonstrated in P 1 . 5 ~
which is of the adaxial leaf surface of Lupinus albus. The outlines
of the epidermal cells are marked by widely spaced and relatively large wax projections.
The centre of each epidermal cell appears to have developed wax projections which are
finer, more angular and more densely compressed than those on the margins of the cells.
The previous evidence presented suggests that these criteria of small size and angularity
indicate an immature surface a t an early stage in its development. But, since the conclusion that the centre of an epidermal cell is less mature than the margins is unlikely,
another explanation must be sought.
Although, as already mentioned, the fine structure of a leaf's surface will persist,
when mature, its final form and density may depend on its previous environmental
history.
Lee & Priestley (1924)noticed that in some plants the thickness of the cuticle increased
as the quantity of available moisture fell and the light intensity rose. More recently
Dorschner & Buchholtz (1966),using artificial shade, indicated that a reduction in the
available sunlight influenced the morphological development of lucerne (Medicago
sativa) growing amongst oats so that the wetting capacity of applied chemical sprays
was increased. Therefore the following experiment was planned to study the effect of a
range of light intensities on the fine structure of the cuticle of peas. All the plants in a
single experiment were grown in the same growth chamber and the different light intensities were achieved by interposing one or more layers of butter muslin between the
light source and the plant. The light intensities were measured a t the level of the second
leaf, the leaf that was used for the experiment, and not a t ground-level.
Peas grown in the dark have leaves which are very small, yellow and shiny and their
surfaces are very difficult to replicate. Their appearance (PI. 6 a )under the electron microscope and their contact angle (68")are reminiscent of dicotyledonous plants which have
no apparent surface wax such as the beet (Beta vulgaris) (Pl. 7 a ) . P1. 6b shows the
adaxial surface of a pea grown a t 900ft.-candles. The surface is completely covered
with fine structure and is remarkably uniform. The wax projections are regular, rarely
more than &,u high, have more or less straight sides, and are closely bunched together.
The individual platelets of the projections are thin and are still mostly transparent to
the electron beam. The over-all picture changes only a little a t 1500 ft.-candles. The
416
BARRIEE. JUNIPER
individual projections themselves are nearly twice aa large in all dimensions and are
opaque to the electron beam but they still have more or less straight sides. At 5000 ft.candles (Pl. 6 d ) development of the fine structure seems to have reached its peak. The
difference is even apparent to the eye in an increased whiteness of the surface &B compared to the pea surface corrcsponding to P1. 6 c .
The individual crystals are only a little thicker than in P1. 6c, but their margins have
developed to such an extent that the background is almost entirely obscured. However,
the contact angle of peas grown in light intensities over the range 5OOO-900 ft.-candles
remains close to 140". This must be due to the whole surface being covered with projections, even at 900 ft.-candles. The lowering of the light intensity incident on pea
leaves within the range that one could expect to encounter in the field seems therefore
unlikely to make much difference to the actual wettability of the surfaces. However,
the differences in the density, the height and the interlocking of the individual projections
a t different light intensities might well be si@cant where aerial weathering was
severe. The less well-developed surfaces would be more severely affected by mechanical
damage, and peas are known to be susceptible to this type of damage. I n this context
the effect of a high wind spccd on the growth of the fine structure of a leaf's surface is
interesting. P1. 7 b shows a n adaxial leaf wrface of a pea from a plant grown in a wind
tunnel with a wind of 25 m.p.h. If this is compared with P1. 6 d of a plant of comparable
age grown in still air, differences are immediately apparent. Although the contact angles
of the two surfaces are similar i t would appear that a high wind speed results in shorter,
thicker and more dense projections from the surface; all these features would tend to
increase resistance to abrasive damage. One of the effects of mechanical damage would
bc to incrwsc the wettability of the surfaces and this may have contributed to thc
enhanced retention noticed by Dorschner & Ruchholtz.
The appearance of these micrographs, particularly when seen in transverse sections
(Yl. 7c) suggests strongly that mechanical damage might be a n important factor in the
wettability of plant surfaces. It is a common observation amongst agronomists that the
amount of mechanical damage inflicted on an individual plant's surface affects the SUBceptibility of those plants to herbicides subsequently applied (see Dewey, Gregory &
Pfeiffer, 1956). "he effect varies from crop to crop, slowly grown plants in general
tending to be more resistant than those grown rapidly. Only some species of plants,
moreover, seem to be susceptible to mechanical damage to their wax covering.
It is very difficult t o relate general observations of this kind to differences observable
in the laboratory. However differences in growth rate do result in differences in the
ultra-structure of the surfam of some plants, and they could be connected with their
response to mechanical damage. For example, P1. 8 a shows the stem surface of a very
rapidly grown cabbage. The individual wax tubes are widely spaced and, as such,
lacking in mutual support, would be very susceptible to mechanical damage. The leaf
surface of a more slowly grown cabbage is shown in P1. 4b. The leaves of cabbages, in
which root growth is severely restricted, are limited in size but develop a thick blue
bloom on the cuticle which is visible under the electron microscope a8 a tangled mass of
tubes, some crushed and flattened and others still intact and erect. There is some evidence, as already mentioned, that separate sites of extrusion may join up with one another
(Pl. 4b) and new isolated sites may develop in between with the result that, in old leaves,
the background is almost completely obscured. Some leaves, therefore, which grow
slowly have a thicker layer of wax projection8 developed on all their surfaces and this
may contribute both to their resistance to mechanical damage and possibly also to the
increased resistance to herbicides observed.
However, different species of plants, as well as the tame plants grown under different
conditions, seem t o react Merently to mechanical damage. Also, if damaged, some
secm to possess powers of recovery, during a t least the early stages of their development.
The differences between species are obvious even to casual examination; the hyacinth
Effectof environmeni on the ultra-structure of plant surf-
417
(Hyacinthw orientalis) and the daffodil (Narcissw pseudonarcissw) lose their 'water
repellent bloom very rapidly, and, only a very short time after leaf emergence, their
surfaces are completely wettable. The cabbage is rather better protected and only old
mature leaves which have been subjected to considerable abrasion are usually wettable.
A very few species, such aa Oxalis m i c u l a t a , retain the ability to repel water droplets
indefinitely. The degree of resistance offered by a plant to mechanical damage could
depend on the composition of the wax of which the outermost layers of its cuticle were
formed or the form taken by the wax projections.
The hardness of a wax will depend on a number of factors, including the conditions
under which it is grown and its rate of growth. However, so very little is known about
the comparative chemistry of plant waxes that it is very di6cult to use such data as are
available. On the other hand, an examination of the fine etructure has proved very
interesting if not conclusive. If we take the extremes of the series, aa far as susceptibility
to damage is concerned (Hyacinthusorientalis and Omlis corniculata),differences in the
projections are immediately apparent. The h e structure of Hyacinthw, orientalis (Pl. 8 b )
is an irregular pattern of very fine sheets of wax, giving the impression that they have
just peeled away from the surface like strips of the bark from a tree. The individual sheets
seem to have no preferred orientation and rarely touch one another. The appearance of
the O d i s surface (Pl. 4 4 is completely different. The individual projections are starshaped and are therefore less likely to be pushed over ; they are so close together as to
make it impossible to see the background and the individual segments of the projections
interdigitate to form a mutually supporting mesh. Although the initial contact angles
of these two surfaces are the same (above 140") the leaf surface of the Hyacinthw, is
readily damaged even by watering from above in the greenhouse and, out of doom,
the surface is usually wettable within a few days of the unfolding of the leaves. The
leaves of the OxdU, even in exposed situations, remain unwettable indefinitely and unlike most species, the yellow and senescent leaves still have a contact angle above 140".
Similar to the O d i s in its resistance to mechanical damage is J u m in$exue (Pl. 8 4 .
In this species the sharply ridged epidermis is covered by a m t h cuticle. The heavily
thickened sclerenchyma below the ridges, the hard cuticle and the vertical positioning
of the leaves combine to make a surface almost impervious to damage. Apart from this
apecial case, in which the p e e morphology of the leaf is the significant factor, the appearance of the micrographs of the surfaces seems to be a good guide to the qualities of thoae
surfaces. The pea, for example (Pl. 6 4 is similar to O m l i s in its fine structure, but the
projections are lw dense and do not interlock to quite the same extent. The pea leaf is
somewhat more susceptible to mechanical damage than Ozalis, but is among the most
resistant of cultivated plants, particularly when grown slowly. Similar in properties
to the pea leaf is the surface of Chrysanthemumsegetum (Pl. 4 a ) ;the entangled mass of
wax tubes is not readily crushed (PI. 8c) nor easily washed away. Similarly, in Bra.98ica
obracea even if the tubes are broken and pushed over they retain enough of their structure to preserve the micro-roughness necessary for a high contact angle. P1. 9 b shows a
cabbage which has suffered severe field weathering and on which considerable quantities
of soot have landed. Although almost all the fine structure of the original surface haa
disappeared, neither the tubes themselves, nor the bases of those tubes are sufficiently
crushed to depress the angle below 140";all the fine structure, it seems, must be eroded
away before the contact angle is reduced. Many species, such as aalanthue nivalis
(PI. 9a) have wax projections on their surfaces which are too widely spaced and too delicate to avoid being flattened or brushed away.
Only a few species have been observed to recover from mechanical damage and reestablish a high contact angle. If the surface of a young leaf of Chrysanthemum segetum
is brushed vigorously the contact angle falls to just below 100". But within 7 days, if the
leaf is not too badly damaged in the initial treatment, the surface regenerates and the
contact angle rises above 140" again. This only occurs if the leaf is damaged before leaf
418
B ~ R ~ E.
I EJUNIPER
expansion has ceased. Brm8ica oleraceu recovers rapidly at first but the ability to recover ceases before leaf expansion ceases. But in the majority of speciea with waxy
surfam recovery does not take placa at all; it has never been seen, for example, in the
LeguminOt3ae.
The present research has revealed, in greater detail, the fine struoture of a part of the
cuticle. It hm not elucidated any further the procesaes by which the cuticle is formed,
and,in fact, this evidence means that we must modify the theoriea of development of the
cuticle put forward by Prieatley (1943) and later by Scott, Hamner, Baker & Bowler
(1968). We must add a complete stage to the process of the development of the cutiole;
a stage which ia distinct from and has apparently no connexion with the formation of the
pectin and the cutin layers. There ia no evidence, moreover, to suggest, as has been put
forward, that the wax ultraetructure of the plant surfaca is connected with plaamodesmata. My observations agree with those of Schiefemtein& Loomis (1966) that there is
as yet no evidence for the existence of definite pores through which the wax is extruded
or migrates. It seems unlikely that the process of wax extrusion is even indirectly
connectcd with plasmodesmata. The density of plasmodesmatd strands recorded is
not above 36/100pa (Esau, 1963). This is much lowcr than the density of distinct
wax projections seen on any of the surfacee which may be up to 400/100pa. Plasmodcsmata have, moreover, rarely been found in epidermal cells. It seems then that
the processes by which the layers of the outicle are formed will have to await both
advances in cuticular chemistry and in techniquea for the sectioning of plant material
for the electron mioroscope.
ACKNOWLEDQEMENTB
The author would like to express his gratitude to Imperial Chemical Industries Ltd.
for financial aesietance in the above research and in the publication of its results.
REFEHENCEB
DEWEY,
0. I%., GREGORY,P. & PEEIFFER,H. K., 1966. Factors af€wting the susceptibility of peas to
seleative dinitroherbicidea. Brit. Weed Control Conf. Proc. 1, 313-27.
DORSCHNER,
K. P. & BUCHHOLTZ,
K. P., 1966. Wetting ability of aqueous herbicidal sprays BR a
factor influencing stands of alfalfa seedlings. Agron. J. 48,59-63.
ESAU,K., 1953. Plccnt Amlomy, v-xii+735 pp., 86 pls, figs. 1.1 20.5. London: Chapman end 11811.
FREY-WYBBLING.
A., 1948. Submicroscqlzic Morphology of Protoplaam and its Derivativce. v-viii+255
pagos, 161 Gge. Amsterdam.
D. E., 1968. The carbon replica technique in the study of the ultrastrucJUNIPER,B. E. & BRADLEY,
ture of leaf surfauea. J . Ultrasttucture Re.9. 2, 16.
JUNIPER,B. P.,1869. "he surfaces of plants. Endeavour, 69, 2&5, 24 figs.
LEE, B. & PEIESTLEY,
J. H., 1924. The plant cuticle. 1. Its structure, distribut,ionand function.
Ann. Bot. 38, 62&45, 12 figs.
MUELLER, L. E., CARR,P. H. & Looxrs, W . E., 1964. The submicroscopic structure of piant surfaces.
Amer. J . Rot. 41, 593-600, 24 figs.
PRIESTLJCY,
J . H., 1943. The cuticle in angiosporms. Bot. Rev. 9 (9), 593-616.
YCHIEFERBTELV, R. H.& LOOMIS,
W. E., 1956. Wax deposits on leaf surfaces. Plust. Physiol. 31,
240-7, 18 fige.
Yrom, F. M., HAMXER,
K. C.,BAKER,
E. & BOWLER,
E., 1958. Electron microscope studies of the
epidermis of Allium cepa. Amer. J . Bot. 45, 448--61, 31 figs.
EXPLANATION OF PLATES 1-9
PLATE
1
a. Adaxial leaf surface of P k m aaliuclm grown in derkneea to second leaf stage. x 1100.
b. The Bame 24 hr. after transfer to light. x 12,400.
c. The E B ~ O48 hr. efter transfer to light. x 12,400.
d. The samo 72 hr. efter trenefer to light. x 12,400.
Jnnrn. Linn. Sue. Bot. l'ol. iifi, .\'u. 3fi7
13. E. Jl:XfPE[{
Plate L
(Faciny p. 41 t\)
.Jnurn . /,inn. Soc. !Jot. Yol. !iu, Nn. :3ti7
B. E.
JU~lPER
Plate 2
.Tourn. Linn. Soc. But. Vol. 5G, Yo. 3H7
.13. K Jl./XII'EH
Plate a
Jonrn. hinn. Soc. Bot. Vol . .'3t.i, No. 367
D. E. JUKirER
Plate 4
Jrm-rn. L1:·n:n. Soc. Bot. Vol. 56. No. :Hli
B. E. JlJ!\Il'ER
Plate 5
Journ. Linn. 8or. Bot. Vol. :36, Yo. :367
B. E.
.TU~IPEH
Plate G
Journ. Linn. Soc. Bot. Vol. 56, No. 3fl7
ll. E.
JU~IPE!t
Plate 7
Journ. Lt:nn. Snc. Rot. Vol. 56, No. 367
13. E. JGKIPEil
Plate 8
Jount. Linn. Soc. Bot. Vol. 56, No. 367
B. E.
JU~IPER
Plate ()
Effect of environment on the uUra-structure of plant surfaces
419
PLATE 2
a. Adaxial leaf surface of Piaum aativum 72 hr. after transfer to light. x 1100.
b. The same 5 days after transfer to light. x 8800.
o. The same 7 days after transfer to light. x 12,400.
d. Abaxial leaf surface 3 days after transfer to light. x 1100.
PLATE
3
a. Abaxial leaf surface of Piaum aativum 4 days after transfer to light. x 1100.
b. The same 4 days after transfer to light. x 8800.
o. The same 5 days after transfer to light. x 8800.
d. The same 5 days after transfer to light. x 1100.
PLATE 4.
a. Adaxial leaf surface of Chrysanthemum segetum. x 12,400.
b. Adaxial leaf surface of Braasioa oleracw va.r. capitata.
12,400.
c. Adaxial leaf surface of BraaBica oleracw va.r. capitata. x 19,200.
d. Adaxial leaf surface of Oxalis corniculata. x 12,400.
x
PLATE 5
a. Adaxial leaf surface of Papaver somniferum. x 8800.
b. Adaxial leaf surface of Kleinia articulaw. x 12,400.
c. Adaxial leaf surface of Lupinus albus. x 1100.
PLATE 6
a. Adaxial leaf surface of Pisum Bativum grown in darkness. x 12,400.
b. The same grown at 900 ft.-candles. x 12,400..
e. The same grown at 1500 ft.-candles. x 12,400.
d. The same grown at 5000 ft ..ca.ndles. x 12,400.
PLATE
7
a. Adaxial leaf surface of Beta vulgaris.
x 1100.
b. Adaxial leaf surface of Piaum sativum grown in wind·tunnelat 25 m.p.h. wind.speed. x 12,400.
o. Adaxial leaf surface of Lupinus albus. The oa.rbon film has been broken on the grid, has bent over,
and has been photographed at right angles to the normal plane of viewing. x 18,000.
PLATES
a. Stem surface of Braaaica oleracw va.r. capitata. x 6600.
b. Adaxial leaf surface of Hyaeinthus orientalis. x 12,400.
c. Adaxial leaf surface of Chrysanthemum aegetum damaged by brushing. x 12,400.
d. Leaf surface of Juncus injlexua. x 12,400.
PLATE
9
a. Adaxial leaf surface of Galanthus nivaliB. x 18,000.
b. Adaxial leaf surface of Braaaica oleracw va.r. capitata grown in the open and heavily contaminated
with soot. x 18,000
22
JOURN. LINN. SOC.-BOTANY, VOL. LVI