Bot. J. Linn. Soc., 63, pp. 313-320. With 5 plates and 1 figure
October 1970
The vestured pits of Eucalyptus regnans F. Muell.: a study usin~
scannin~ electron microscopy
G. SCURFIELD, F.L.S.
C.S.I.R.O., Division of Forest Products, S. Melbourne, Victoria, Australia
AND
S. R. SILVA
Australz'an Defence Scientific Service, Defence Standards Laboratories, Commonwealth
Dept. of Supply, Maribyrnong, Victoria, Australia
Accepted for publication November 1969
Scanning electron microscopy has been used to examine the surface architecture, before and
after various chemical treatments, of the pits in the walls of vessels, vasicentric and fibre
tracheids, and parenchyma cells, which together make up the wood of Eucalyptus regnans.
The treatments included water at 150°C under pressure, hydrofluoric acid, delignifying
agents and potassium permanganate. All bordered pits were vestured; half-bordered pits
were vestured, partially vestured or non-vestured. No distinction could be made between
warts and vestures on morphological or chemical grounds. An hypothesis is advanced which
relates vesture formation to prolongation of the activity of the protoplast in pits as the cells
die. Vestures, on the basis of this hypothesis, could be regarded as enlarged or conglomerate
warts.
CONTENTS
PAGE
313
314
314
319
319
Introduction
Methods .
Results and discussion
Acknowledgement
References
INTRODUCTION
The extent to which studies of the effects of chemical treatments on plant cell
walls can provide information as to the structure and properties of such walls is a
question of general interest. It has been considered in relation to the structure of the
walls of reaction wood tracheids. The advantages of scanning electron microscopy
in such studies have been demonstrated (Scurfield & Silva, 1969a, b). We are
concerned here with using scanning electron microscopy to investigate the surface
architecture, before and after various chemical treatments, of the pits in the walls of
the vessels, vasicentric and fibre tracheids and parenchyma cells which together
make up the wood of Eucalyptus regnans.
313
314
G. SCURFIELD AND S. R. SILVA
METHODS
Transverse, oblique and longitudinal radial and tangential sections, about 100 11-m
thick, were cut from the mature sapwood of a large tree of Eucalyptus regnans. They
were dried in vacuo at room temperature. They were then mounted on standard
stubs and coated with Au (calculated maximum thickness 40 nm) in a high vacuum
coating unit fitted with two evaporating sources and specimen rotation to provide a
layer of uniform thickness. Specimens were examined with the Cambridge scanning
electron microscope (Stereoscan Series I).
Longitudinal tangential and radial sections similar to the above were also examined
after being subjected to one of the following chemical treatments:
(a) distilled water at 150°C under pressure for 2 h in a stainless steel reaction
vessel;
(b) saturated chlorine water (5 min) followed by 2% NaOH (1 min) at room
temperature, repeated until sections were colourless;
(c) glacial acetic acid/30% hydrogen peroxide (1/1 vjv) at 90°C until sections were
colourless;
(d) 14 % nitric acid at 55°C for 1 h, followed by 14% nitric acid at 95°C for
1} h, and then 3% NaOH at 95°C for 1 h (Kalisch, 1967) (sections examined after
each stage) ;
(e) hydrofluoric acid (Cote et al., 1968);
(f) 2% potassium permanganate for 15 min at room temperature.
RESULTS AND DISCUSSION
Vessels in the wood of Eucalyptus regnans are solitary. Light microscopy indicates
that vestured bordered pits occur between such vessels and the vasicentric tracheids
surrounding them. They also occur between adjacent vasicentric tracheids. However,
it is difficult to determine by this means whether the bordered pits occurring between
vasicentric and fibre tracheids are vestured. The same is true of the bordered pits
occurring between adjacent fibre tracheids, though Bailey (1933) found what he
termed 'papillary projections from the margins of both the inner and outer apertures'
of such pits in Eugenia dichotoma. In the case of the half-bordered pits which occur
between vessels or vasicentric tracheids and adjacent xylem or ray parenchyma cells,
it is generally assumed that these are vestured only on the vessel or vasicentric tracheid
side. Bailey (1933), Cote & Day (1962) and Yamanaka & Harada (1968) have illustrated
this feature of half-bordered pits in members of the Dipterocarpaceae.
Scanning electron microscopy indicates that the bordered pits connecting
vasicentric and fibre tracheids in Eucalyptus regnans are, in fact, vestured (Plate lA).
So too are the bordered pits connecting adjacent fibre tracheids (Plates 1 B, C and
3D). In these cases, the smallness of the pit apertures, plus the fact that the vestures
are confined to the entrance of the pit canal and do not extend beyond the pit aperture
to the extent that they do in vessels (Plates 3 F and 4A) would account for the
difficulty of observing them with the light microscope.
In the case of half-bordered pits occurring between vessels or vasicentric tracheids
and parenchyma cells, the border may be vestured, partially vestured or non-vestured
(Plate 1D, E, F). Failure to observe vestures in association with tyloses (Faster, 1967)
VESTURED PITS OF EUCALYPTUS REGNANS
315
would be accounted for if tylosis formation were limited to the non-vestured pits.
Both the size of the apertures and number of half-bordered pits are of interest in any
consideration of the movement of liquids, for example, between vessel and ray parenchyma cells. There are fewer half-bordered than bordered pits in the vessel walls
of E. regnans. The apertures of the former, despite considerable variation in size,
are several times larger than those of bordered pits. However, from the point of view
of liquid movement from the vessels, it is uncertain whether more could pass in a
given time through half-bordered than through bordered pits, a limiting factor being
the permeability of the pit floors.*
Pit
floor
S3-warted
Pit rim with
wart-like
vestures
S3-warted
---r--~
VESSEL
VAS! CENTRIC
TRACHEID
FIGURE 1. Diagram of a vestured bordered pit of Eucalyptus regnans. Secondary wall layer 81
is cut back to show the underlying primary wall P.
The appearance in surface view of radial longitudinal sections through bordered
pits connecting vessel and vasicentric tracheid can best be interpreted in terms of
the diagram of such a pit shown in Fig. 1. This appearance depends on the plane of
section, or on the extent to which stripping of wall lamellae has occurred. Plates
2B-F and 3A-C show surface views of walls variously stripped of lamellae observed
in a section treated with hydrofluoric acid: Plate 2B-passing near the lumen
surface of the vessel; Plate 2C-approaching the vessel pit chamber; Plate 2D,Eapproaching the pit floor, the floor being lifted in the pits labelled p and almost
entirely removed in the pit labelled b in 2E; Plate 2F-the pit floor and, therefore,
presumably the inner surface of the primary wall of the vessel; Plate 3A,B-the pit
floor partially or entirely removed to reveal the pit chamber and vestures of the pit in
the vasicentric tracheid wall; and Plate 3 C-removal of the pit border and, in the pit
arrowed, most of the vestures also, to reveal the pit aperture opening into the
vasicentric tracheid lumen.
• The term 'pit floor' is used in place of the more usual 'pit membrane'. The reason has been given
elsewhere (Scurfield, 1967 a).
316
G. SCURFIELD AND S. R. SILVA
The persistence of a microfibrillar texture after treatment with hydrofluoric acid
(Plates 2B to 3 C), applied according to the method of Cote et al. ( 1968), indicates
incomplete removal of cellulose. Cote et al. claimed to have achieved removal of all
cell wall constituents except lignin from the walls of conifer reaction wood tracheids
by this means. It would seem that the conditions of treatment will need to be modified
in order to achieve the same end result with vessel walls, for hydrofluoric acid attacks
such walls. This is indicated, for example, by the surface texture of the pit floors
shown in Plate 2F and the changed appearance of vestures and warts (see below) on
the inner surfaces of vessels. The floors of pits in untreated sections are felt-like, an
appearance consistent with their underlying disperse or random microfibrillar texture
(see, for example, Schmid, 1965). The retention of something approaching this texture
by the floors of pits, such as those marked X in Plate 3 B, after treatment with hydrofluoric acid is unusual. However, these floors are seen to be breaking up also. Certainly
it would be anticipated that pit floors, by virtue of the fact that they appear to be
relatively poor in lignin compared with the rest of the cell wall (Scurfield, 1967 a),
would be especially susceptible to attack by hydrofluoric acid.
Two other structural features are to be noted: (a) The microfibrils surrounding
the pit chamber or, in other words, the inner surface of the pit border, are circularly
arranged (Plate 2E). This is a well-known feature of bordered pits (see, for example,
Liese, 1965). (b) The vestures are largely confined to the pit canal, being especially
prominent about its inlet into the pit chamber, and its outlet into the cell lumen.
Not all the inner surface of the pit chamber is vestured: a rim bearing a few wart-like
vestures or none at all (arrows in Plates 2E and 3B,D) separates the floor from the
vestured roof of the pit chamber. As secondary wall layer S1 contributes little or
nothing to the pit chamber wall (Fig. 1 and many published electron micrographs,
for example those of Yamanaka & Harada, 1968), vestures apparently arise from S2.
Their possible origin from S3 will be considered below.
Essentially the same features as those outlined above characterize the bordered
pits connecting adjacent vasicentric tracheids, or vasicentric and fibre tracheids, or
adjacent fibre tracheids. There are some differences, but these might be regarded as
quantitative rather than qualitative. Pit apertures, for example, may differ in size
and shape and in the orientation of their major axes with respect to the longitudinal
axis of the cells (compare Plates 1 A, C and 5 B). Pit chambers vary in size (compare
Plates 1B and 3 B), and pit vestures in degree of structural complexity (compare
Plate 1 A and F).
Special consideration needs to be given to the inner (lumen) surfaces of the vessels,
vasicentric and fibre tracheids. These surfaces are warted. However, the number of
warts which occur and the density with which they are packed together varies widely
(compare Plates 1 C and 3 E). The warts are believed to be covered by a 'membrane'
derived from the denatured tonoplast and/or plasma membrane (Wardrop & Davies,
1962). Such a 'membrane' is shown in Plates 2A and 4B (labelled m). Judging from
Plate 2A, this 'membrane' may cover, not only warts, but pit apertures also. However,
the latter do not appear to be 'membrane' -covered in untreated vessels (Plate 3 E),
though Wardrop et al. (1963) and Schmid & Machado (1964) have reported that
individual vestures may be covered.
VESTURED PITS OF EUCALYPTUS REGNANS
317
This brings us to the question of the nature and origin of warts and vestures.
Bailey (1933), using the light microscope, described vestures as minute outgrowths
from the surface of the secondary wall surrounding the pit chambers. Similar outgrowths (now termed 'warts') were said to occur on the inner surfaces of the vessels.
These observations have since been confirmed by Cote & Day (1962), Wardrop et al.
(1963), Schmid & Machado (1964) and Yamanaka & Harada (1968), using the transmission electron microscope. Cote & Day believed that the vestures and warts in
hardwood vessels were similar in nature and origin. Wardrop et al. also commented
upon the resemblance of the form of warts (in conifer tracheids) and vestures (in
vessels of a species of Eugenia). Both were regarded as elaborations of the cell wall,
and both were believed to be covered with a denatured cytoplasmic membrane.
Schmid & Machada (results reiterated by Schmid, 196S), however, after observing
what they regarded as warted vestures in Plathymenia foliolosa, defined vestures as
outgrowths of the cell wall formed by living cells, warts as 'remnants of the dead
protoplast', and the 'warty layer' as consisting of plasma membrane and tonoplast
with particles enclosed between. This interpretation of warts is difficult to maintain
in the face of evidence, such as that of Wardrop & Davies (1962), that warts, like
vestures, are outgrowths of the secondary cell wall.
Present evidence (Plates 1A,E and 4A, for example) confirms the observation of
Bailey that vestures are indeed protuberances from the cell wall which not only
occupy the pit apertures, but also spill out of these into the lumina of the vessels.
There the vestured areas merge with those bearing warts (Plates 3F and 4A,D).
In the transition region between the two it is difficult to decide whether surface
protuberances are vestures or conglomerate warts. Warts, in other words, seem to
differ from vestures merely in size and degree of aggregation. Both appear as outgrowths of what is presumably secondary wall layer 83. It is not surprising, therefore,
that Schmid & Machada observed what they termed 'warted vestures' in Plathymenia.
Apart from their structural similarity, warts and vestures respond in much the
same way to the chemical treatments employed here. Vestures swell on treatment
with water at 1S0°C under pressure. It is uncertain whether warts also swell (Plate
4C), but neither they nor vestures are dissolved. Hydrofluoric acid attacks both
warts and vestures (compare the warted surfaces in Plate 4D with that in Plate 3E).
As regards the effects of delignifying reagents, Cote & Day (1962) reported that
acidified sodium chlorite at 7S°C for four hours caused little degradation of either
warts or vestures. This is surprising in view of the results obtained here with
delignifying reagents: chlorine water-sodium hydroxide, glacial acetic acid + hydrogen
peroxide and nitric acid-sodium hydroxide all remove warts and vestures (compare
Plates 4E, 4F to SB and SC-E with Plate 3E). Glacial acetic acid+ hydrogen
peroxide appears to cause less severe degradative changes to warts and vestures than
nitric acid (compare Plate SB,D). However, the final stage (treatment with 3%
sodium hydroxide) of the nitric acid-sodium hydroxide process frees surfaces of both
warts and vestures, leaving them as shown in Plate 4 E.
Warts appear to be rather more easily removed than vestures by either glacial acetic
acid+ hydrogen peroxide (Plates 4F and SA) or nitric acid (Plate SD,E). The
318
G. SCURFIELD AND S. R. SILVA
difference, being quantitative rather than qualitative, probably reflects a difference in
structural complexity of warts and vestures (see below) rather than in their chemical
composition. It is to be noted that the warts on the inner surfaces of conifer tracheids
can also be removed by delignifying agents, such as chlorine water-sodium hydroxide
or glacial acetic acid + hydrogen peroxide (Scurfield & Silva, 1969 b).
The effects of glacial acetic acid + hydrogen peroxide are of interest from another
point of view. The warts and vestures which by this means are separated from the
underlying cell walls remain undissolved as more or less spherical particles. Possibly,
therefore, treatment of sections with glacial acetic acid-hydrogen peroxide, followed by
centrifugation or filtration, offers a means of isolating warts and vestures from cell
walls. This possibility is currently being examined, though, from the point of view
of obtaining warts and vestures for chemical analysis, mechanical means of isolation
are to be preferred.
Something is known of the interaction of potassium permanganate and cell wall
constituents (see, for example, Brauns & Brauns, 1960). Little of this information,
however, concerns the interaction between such constituents and 2% potassium
permanganate at room temperature, conditions under which potassium permanganate
has been widely used as a fixative of plant cells for electron microscopy. One such
interaction is the elimination of -CH=CH-CHO groups responsible for positive
phloroglucinol-HCl tests for lignin in plant cell walls, and the creation of further
aldehyde groups (presumably by oxidation of cell wall polysaccharides) (Scurfield,
1967 b). Whatever the underlying chemistry, Plate 5 F indicates that the treatment
results in the deposition of considerable amorphous material on wall surfaces. No
doubt some of this consists of manganese oxides. Similar effects on the walls of
tracheids in reaction and normal wood of conifers have been observed (Scurfield &
Silva, 1969b). Scurfield & Silva mentioned that an explanation of why potassium
permanganate is somewhat capricious as a fixative of living wood cells might include
consideration, not only of chemical interaction with wall constituents, but also of the
products of such interaction preventing movement of the fixative through the cell
walls. However, this may be of lesser importance if the considerable cracks which
develop in such walls around the vestured pit apertures (Plate 5 F) are not, in fact,
artefacts of vacuum drying during specimen preparation. It is also possible that the
separation of vestured and warted areas of the inner surfaces of vessels after the first
stage of the treatment with nitric acid (Plate 5 C) is an artefact.
Given no firm ground for a belief that warts and vestures differ in chemical composition, the question as to what 6is composition might be remains. The results merely
indicate that both warts and vestures are insoluble in water at 150°C under pressure,
are only slightly attacked by hydrofluoric acid and possibly by 2% potassium
permanganate, but are detached and/or dissolved by delignifying agents. This leaves
us at present with little other than the conclusion that lignin might be a component
of warts and vestures. This lignin might be responsible for the absorption by warts
and vestures of ultra-violet light (Wardrop, 1964).
The morphological and chemical similarity of warts and vestures and their location
as described here invite speculation as to their mode of origin. It has been suggested
elsewhere (Scurfield & Silva, 1969 b) that a warted surface might be rega-rded as a
VESTURED PITS OF EUCALYPTUS REGNANS
319
replica of the plasma membrane surface, the warts corresponding to invaginations
in the latter through which wall materials were being actively secreted at the time the
cell died. Pit chamber walls, on the basis of this assumption, should be warted.
Assume, however, that transfer of wall materials through invaginations in the plasma
membrane which correspond with warts, present or in the process of formation on the
walls of pit chambers and canals, is in some way prolonged. Massive vestures of the
type occurring in Gymnocladus dioicus (Cote & Day, 1962) might be built up. Such
vestures, on this basis, could be termed 'enlarged warts'. On the other hand, continuing transfer of wall materials through invaginations undergoing rapid progressive
relocation could produce branching, bead-like vestures of the type shown in Plates
3F and 4A. These might be termed 'conglomerate warts' or 'proliferating warts'.
Intermediate forms, including the so-called warted vestures observed by Schmid &
Machado (1964) in Plathymenia foliolosa, might be expected to occur in some cells
or species. As to the way in which local activity of the protoplast might be prolonged,
it is possibly related to the occurrence of intercellular connections (plasmodesmata)
between the pits, or to the existence of pit canals of narrow aperture retarding protoplast withdrawal or perhaps breakdown.
ACKNOWLEDGEMENT
We are grateful to Dr F. A. Fox, Chief Superintendent, and Mr J. A. Macdonald
of Defence Standards Laboratories, Maribyrnong, for greatly facilitating our
cooperation.
REFERENCES
BAILEY, I. W., 1933. The cambium and its derivative tissues. VII. Structure, distribution, and diagnostic significance of vestured pits in dicotyledons. J. Arnold Arbor., 14: 259-273.
BRAUNS, F. E. & BRAUNS, D. A., 1960. The Chemistry of Lignin. Suppl. vol. New York: Academic Press.
CoTE, W. A. & DAY, A. C., 1962. Vestured pits-fine structure and apparent relationship with warts.
Tappi, 45: 906-910.
CihE, W. A., DAY, A. C. & TrMELL, T. E., 1968. Distribution of lignin in normal and compression
wood oftamarack. Wood Sci. Technol., 2: 13-37.
FosTER, R. C., 1967. Fine structure of tyloses in three species of the Myrtaceae. Aust. J. Bot., 15:
25-34.
KALISCH, J, H., 1967. Nitric acid pulping. Tappi, 50 (12): 44A-51A.
LIESE, W., 1965. The fine structure of bordered pits in softwoods. In Cote, 'vV. A. (ed.), Cellular ultrastructure of woody plants. Syracuse, N.Y.: Univ. of Syracuse Press.
ScHMID, R., 1965. The fine structure of pits in hardwoods. In Cote, W. A. (ed.), Cellular ultrastructure
of woody plants. Syracuse, N.Y.: Univ. of Syracuse Press.
SCHMID, R. & MACHADO, R. D., 1964. Zur Entstehung und Feinstruktur skulpturierter Hoftlipfel
bei Leguminosen. Planta, 60: 612-626.
ScuRFIELD, G., 1967 a. The ultrastructure of reaction wood differentiation. Holzforschung, 21: 6-13.
ScuRFIELD, G., 1967b. Histochemistry of reaction wood differentiation in Pinus radiata D. Don.
Aust. J. Bot., 15: 377-392.
ScuRFIELD, G. & SILVA, S. R., 1969a. Scanning electron microscopy applied to a study of the structure
and properties of wood. Proc. 2nd Annual Scanning Electron Microscopy Symposium, Chicago, 1969.
Chicago: I. I. T. Research Institute.
ScuRFIELD, G. & SrLVA, S. R., 1969b. The structure of reaction wood as indicated by scanning
electron microscopy. Aust. J. Bot., 17: 391-402.
WARDROP, A. B., 1964. The structure and formation of the cell wall in xylem. In Zimmermann, (ed.),
Formation of Wood in Forest Trees. Syracuse, N.Y.: Univ. of Syracuse Press.
WARDROP, A. B. & DAVIES, G. W., 1962. Wart structure of Gymnosperm tracheids. Nature, Lond.,
194: 497--498.
WARDROP, A. B., INGLE, H. D. & DAVIES, G. W., 1963. Nature of vestured pits in angiosperms. Nature,
Lond., 197: 202-203.
YAMANAKA, K. & HARADA, H., 1968. The ultrastructure of vessel walls in certain species of Dipterocarpaceae. Bull. Kyoto Univ. Forests, No. 40: 293-300.
320
G. SCURFIELD AND S. R. SILVA
EXPLANATION OF PLATES
PLATE
1
A. Vestured pit in the wall of a vasicentric tracheid viewed from the lumen side. x 4560.
B. Vestured pit in the wall of a fibre tracheid viewed from the outer surface. x 10,000.
C. As in B, but viewed from the lumen side. x 9000.
D. Half-bordered pits between a vessel and ray parenchyma cells. The pits are vestured, partially
vestured or non-vestured on the vessel side. x 1850.
E. Partially vestured half-bordered pits. x 4560.
F. Vestured half-bordered pit. x 9000.
PLATE
2
Figures are parts of a section pretreated with hydrofluoric acid. They show different planes of section
through a vestured bordered pit connecting a vessel and a vasicentric tracheid.
A. Lumen surface of a vessel showing a 'membrane' (m) overlying a warted surface. x 5000.
B, C. Views of vestured pits in different planes, the planes created by the stripping of wall lamellae.
The planes begin at the lumen of the vessel (B) and approach successively nearer the pit floors shown
in F. B x 4000; C x 5400.
D, E. Pit floors are lifted in the pits labelled p; the pit floor is almost entirely removed from the pit
labelled bin E. Note in E also that the microfibrils surrounding the pit chamber are circularly arranged
(pit labelled b), and that there are wart-like vestures (arrowed) on the rim between the pit floor and
the pit roof. x 5000.
F. The pit floor and, therefore, presumably the inner surface of the primary wall of the vessel. The
roughened surfaces of the pit floors result from chemical attack (compare surfaces marked X in
Plate 3B. x 5000.
PLATE
3
A-D. Further planes of section through bordered pit illustrated in Plate 2.
A, B. Pit floors partially or entirely removed to reveal the chambers and vestures of pits in the vasicentric tracheid wall. The pits in B have rims which usually bear a few wart-like vestures. x 4600.
C. Removal of the pit borders and, in the pit arrowed, most of the vestures also, to reveal the pit
aperture opening into the lumen of the vasicentric tracheid. x 4600.
D. Vestured pit in the wall of a fibre tracheid. Note in this, as in Plate 1 B, that the vestures occupy
the roof of the pit chamber, a rim bearing wart-like vestures (arrowed) separating the roof from the
pit chamber floor. x 5600.
E. The lumen surface of a vessel showing warts and vestures, the latter overlying pit apertures. x 4600.
F. Enlarged view of vestures shown in E. Note their beaded appearance indicating a conglomerate
structure. x 9000.
PLATE4
A. As in Plate 3F. x 9000.
B. Part of the lumen surface of a vessel treated with water at 150° C under pressure. The warted lining
of the vessel appears as a 'membrane' (m) on the left of the figure. x 4000.
C. Effect of water at 150° C under pressure on the warts and vestures on the inner surface of a vessel.
X 5000.
D. Effects of hydrofluoric acid on the warts and vestures on the inner surface of a vessel. Compare
with Plate 3E. x 5400.
E. Inner surface of a vessel following removal of warts and vestures by treatment with chlorinesodium hydroxide. Similar surfaces remain after the third of the stages in the process involving nitric
acid (see Plate 5 C-E). x 4600.
F. Stages in the separation and dispersal of warts and vestures from the inner surface of a vessel wall
following treatment with glacial acetic acid-hydrogen peroxide. Note the groups of rather larger
particles arrowed. x 4400.
PLATE
5
A, B. As in Plate 4F showing separation of warts and vestures following treatment of vessels with
glacial acetic acid-hydrogen peroxide. A x 9000; B x 4500.
C, D. Inner surfaces of vessels treated with 14% nitric acid at 55°C for one hour. Both vestures and
warts undergo chemical attack. C x 5100; D x 4900.
E. Surface of a vessel following treatment with nitric acid at 55°C for one hour and then at 95°C
for 90 minutes. Warts are removed, but sponge-like remnants of vestures remain. Vesture remnants
are here seen in the apertures of half-bordered pits. x 4600.
F. Inner surface of a vessel treated with 2% potassium permanganate. Note the extensive deposition of
amorphous material and the tendency for cracks to develop around vestured areas which mask pit
apertures. x 5200.
Bot . .'J. Linn. Soc., 63 (1970)
G. SCURFIELD
AND
S. R. SILVA
Plate 1
(Facing p. 320)
Bot.]. Linn. ,)'oc., 6:3 (1 Y70)
G. SCL'HF IELD
AND
8. R. SILVA
Plate 2
Bot.]. Linn. Soc., 63 (1970)
G. SCURFIELD
AND
S. R. SILVA
Plate 3
Bot. J. Linn. Soc., 63 (1970)
G. SCURFIELD
AND
S. R. SILVA
Plate 4
Bot. J. Unn. Soc., 63 (1970)
G. SCURFIELD
AND
S. R. SILVA
Plate S