50 
PACIFIC SCIENCE, Vol. XIX, January 1965 
hypodermal cells put out tylose-like protuber- 
ances which fill the substomatal chamber. These 
invaginations may eventually become thick- 
walled and pitted. Positive lignin reactions by 
which Kofler recognized these stomata are ap- 
parently a property of the resinous material 
which initiates these changes, although walls 
of hypertrophied hypodermal cells may subse- 
quently become lignified. Such occluded stomata 
are very irregular in their distribution, often 
being localized. I have observed them in most 
species examined, although Kofler lists a number 
of species in which they were not observed. This 
is probably not significant taxonomically, since 
the potentiality for their development in old 
leaves possibly exists in all species. Whether 
they are pathological or not is not known. 
( ii ) Variation within a single leaf. Discussion 
of epidermal papillosity has so far dealt only 
with cells next to stomata. Papillae are some- 
times restricted to cells in the vicinity of sto- 
mata, as in P. candelabrum and P. whitmeeanus , 
but are more usually distributed, either uni- 
formly or nonuniformly, over the whole abaxial 
epidermis. Papillae associated with stomata are 
usually taller than those elsewhere. When they 
are uniformly distributed papillae occur equally 
in costal and intercostal regions, although costal 
are almost invariably lower than intercostal pa- 
pillae and are equally developed on all cells (e.g., 
P. erinaceus and P. patina). Otherwise they are 
restricted to intercostal regions. A striking and 
not infrequent condition is for epidermal papil- 
lae to be restricted so that they form a distinct 
reticulum in surface view, with strands of the 
"network” meeting about the stomata (e.g., P. 
capitellatus and P. utilis, Fig. 29). In general, 
specialisation of epidermal papillae closely par- 
allels specialisation of stomata, although anom- 
alous instances where it does not are described 
below. 
Stomata are very constant in structure through- 
out a single leaf surface, but adaxial may differ 
strikingly from abaxial. Adaxial stomata vary 
in number but are always fewer than abaxial. 
They are always unspecialized and never appre- 
ciably sunken, even in species with very elab- 
orate abaxial stomata. Consequently, in these 
species the difference between adaxial and abax- 
ial stomata is very striking (cf Figs. 39, 41). 
(iii) Variation throughout a single individ- 
ual. The trend in stomatal elaboration demon- 
strated throughout Pandanus is partly or wholly 
demonstrated by a single individual in many 
species. This is because seedling leaves and the 
first leaves on each renewal branch of the sym- ( 
podium always possess unspecialized stomata. 
Thereafter, on subsequent transitional leaves or 
scale leaves there is a gradual increase in stoma- 
tal elaboration culminating in stomata of maxi- 
mum elaboration developed by a particular 
species. This maximal condition appears first on 
the first true foliage (or adult) leaves of a shoot j| 
(Fig. 1). Thus on a shoot capable of developing 
elaborate stomata, a long transitional series of 
stomatal types can be demonstrated in the scale- • 
leaf series; otherwise, where the species does not 
develop specialized stomata the range of types 
on a single shoot may be limited, or there may 
be only one type. This concept is illustrated 
diagrammatically in Figure 52. From this it is 
evident that each species of Pandanus has a 
maximum potential for stomatal elaboration 
which is achieved gradually on each new shoot. 
In some species (those which bear Class 5 sto- 
mata) the potential is great; in others (those 
which bear lower class stomata) the potential is 
limited. Many species have no potential for 
stomatal elaboration. That this maximum poten- 
tial is always fully expressed on adult foliage 
leaves is clear from examination of many samples 
of a single species from different sources. Thus 
P. utilis always has stomata of the type illus- 
trated in Figures 28-30 on its adult foliage. 
Associated with the frequent increase in stom- 
atal complexity on successive leaves of a single 
shoot is an increase in stomatal number. Pro- 
phylls always have very diffusely distributed 
stomata, in successive scale leaves they become 
dense, and a more or less constant value is 
achieved in normal foliage leaves. This is a 
genuine increase in stomatal index, since epi- 
dermal cell size is quite uniform throughout this 
range of leaf types. 
The pattern of stomatal variation described 
above is familiar in many other plants (e.g., 
gymnosperms; Florin, 1931). It is easy to dem- 
onstrate in Pandanus because of the relatively 
simple linear sequence of increasing stomatal 
complexity and the constancy of shoot construc- 
tion which makes leaf categories easy to recog- 
nize ( Figs. 1, 52 ) . 
The patterns of variability in stomata have 
