Stomatal Structure in Pandanaceae — TOMLINSON 
39 
England, have also been examined. The culti- 
vated material was in many instances unnamed 
and was used largely to confirm observations on 
named species and to provide large samples for 
studies in stomatal variability. Observation on 
unnamed species, with few exceptions, has not 
been tabulated in this account. A full list of 
named material and sources is given in the 
appendix. 
Only simple technical methods have been 
used. Dried material was restored to a consist- 
ency suitable for anatomical study by boiling for 
several minutes in water to which a little Clorox 
was added. This revived material was stored in 
formalin-acetic-alcohol and proved quite satis- 
factory for anatomical study. Some distortion 
which could not be eliminated by the reviving 
technique did not obscure anatomical details. 
This point is emphasized, because it means that 
stomatal studies in Pandanaceae can proceed 
satisfactorily using herbarium material. Fresh 
material has been examined either unfixed or 
fixed in formalin-acetic-alcohol. 
Preparations showing the surface layers in 
surface view were made by the simple scraping 
technique employed at the Jodrell Laboratory 
and described in detail by Metcalfe (I960: lx). 
Such preparations were either made permanent 
in Canada Balsam, after staining in safranin and 
Delafield’s haematoxylin, or were examined as 
temporary mounts in chlor-zinc-iodide. All ma- 
terial to be sectioned was desilicified by soaking 
overnight in 50% hydrofluoric acid, followed by 
prolonged washing in running water. Freehand 
sections of the demineralized but unembedded 
material, in 70% alcohol, were cut at 10-20 g in 
transverse and longitudinal sections on a Reich- 
ert sliding microtome. Most observations were 
made on sections in temporary glycerine mounts, 
either unstained or after treatment with a vari- 
ety of temporary stains, such as phloroglucin 
and concentrated hydrochloric acid, Sudan IV, 
chlor-zinc-iodide, iodine-potassium iodide, and 
70% sulfuric acid. A few permanent prepara- 
tions of the freehand sections were made by a 
method described elsewhere (Tomlinson, 1961: 
5). 
Illustrations (Figs. 8-51) are from camera 
lucida drawings. These are somewhat stylized 
because of some persistent distortion in dried 
material and because it was often possible to cut 
only thick sections. This is quite an advantage 
since they allowed a complete three-dimensional 
picture of stomata to be built up from optical 
sections in three planes at right angles. 
GENERAL MORPHOLOGY OF PANDANACEAE 
This has been described by Schumann (1897), 
Warburg (1900), and Schoute (1903, 1906) and 
summarized briefly by Tomlinson ( 1964) . Some 
knowledge of growth habit and branching in 
Pandanaceae is essential for an understanding of 
variation in stomatal structure throughout a 
single individual. Early branching begins inde- 
pendently of flowering, but later branching is 
regular, sympodial, and largely dependent upon 
flowering. Lateral branches then arise below and 
replace a parent axis, growth of which is ended 
by its conversion into a terminal inflorescence. 
Eviction of terminal buds by one or more laterals 
is a method of branching typical of plants with- 
out secondary tissue (Schoute, 1906; Tomlinson, 
1964). In Pandanaceae each lateral renewal 
branch in these sympodia bears a similar se- 
quence of leaf forms ( Fig. 1 ) . The first leaf on 
a branch is always a short, bicarinate prophyll in 
the adaxial (adossierte) position. This is suc- 
deeded by a number of scale leaves, each suc- 
cessively longer than its predecessor, forming a 
gradual transition to the normal foliage leaves. 
Length of foliage leaves is fairly constant, al- 
though distal foliage leaves, close to the inflores- 
cence, are short. Renewal buds, one or more of 
which grow out to form the next segments of the 
sympodium, are prominent in the axils of these 
distal leaves. Change of the vegetative into a 
reproductive axis is marked by elongation and 
narrowing of internodes. Inflorescence leaves, 
which are short foliage leaves with a narrow in- 
sertion on the lowest nodes of the inflorescence, 
may be distinguished (Schumann, 1897). Be- 
yond them is a rapid transition to short, color- 
less bracts. The over-all leaf sequence illustrated 
diagrammatically in Figure 1 for one sympodial 
segment of a small Pandanus is characteristic 
for all Pandanaceae, although the number of 
leaves on each segment varies considerably, even 
within a single individual. 
Foliage leaves are lanceolate. In Pandanus and 
