44 
neighbouring cells. Stomata which have no asso- 
ciated papillae represent the unspecialized state. 
A variety of types with gradually increasing 
elaboration of stomata can be recognized, cul- 
minating in stomata completely obscured by 
overarching papillae. In this continuous series a 
number of arbitrary types have been selected, 
each successive type representing an advance in 
specialization over the preceding one. However, 
a complete series of transitional types can be 
found connecting the arbitrary classes. Pandanus 
has the most variation. Sararanga has unspe- 
cialized stomata. Freycinetia forms rather a dif- 
ferent class and is discussed separately. 
(a) Pandanus and Sararanga 
Class 1: Unspecialized stomata (Figs. 8-11, 
19, 49-51). Each stoma has two guard cells, each 
guard cell more or less symmetrical in transverse 
view, with two equal cutinized ledges, each ledge 
situated above thickenings of the front wall 
(Figs. 9, 19). The cell lumen is wide and only 
slightly dumbbell-shaped in longitudinal view. 
Guard cells and lateral subsidiary cells are deeper 
than other epidermal cells, but not sunken. 
Lateral subsidiary cells are thin-walled and con- 
spicuously different from normal epidermal cells. 
Terminal subsidiary cells are short but other- 
wise less well differentiated from normal epider- 
mal cells (Fig. 8). Subsidiary and neighbouring 
cells are never elaborated, apart from slight over- 
arching of lateral by terminal subsidiary cells. 
This type of stoma has been recorded in the 
following species: 
Sararanga 
S. philippinensis S. sinuosa 
The stomata in the two known species of Sara- 
ranga are therefore wholly unspecialized (Figs. 
49-51). 
Pandanus 
PACIFIC SCIENCE, Vol. XIX, January 1965 
P. dubius P. rockii 
P. odoratissimus var. P. tectorius 
laevis P. veitchii 
Solla (1884) records them in: 
P. amarillifolius 
P. cuspidatus 
P. furcatus 
P. javanicus 
P. pedunculatu . 
P. reflexus 
P. stenophyllus 
P. veitchii 
and in six unnamed species. 
In subsequent stomatal classes, guard cells are 
identical in general structure, although they may 
vary considerably in size (cf Figs. 8, 10); an 
over-all range from 1 5-40 g was observed in the 
material examined by me, corresponding closely 
to the range described by Solla. 
Class 2: Papillose lateral subsidiary cells (Figs. 
12-15). The construction described above is re- 
peated, but with the addition of a row of 4-6 
prominent papillae on the outer surface of each 
lateral subsidiary cell. There is no other stomatal 
elaboration, except for a tendency for terminal 
to overarch lateral subsidiary and guard cells to 
a greater extent than in Class 1 (Fig. 13). De- 
gree of stomatal specialization commonly varies 
on a single leaf. For example, in material of 
P. boninensis and P. odoratissimus both Class 
1 and Class 2 stomata were observed on the 
same leaf, together with intermediate stomata 
in which papillae occurred on one or another of 
the two lateral subsidiary cells belonging to a 
single stoma (Figs. 12, 14). A full row of papil- 
lae is always developed, never isolated or re- 
duced numbers of papillae. Class 2 stomata have 
been observed in: 
P. baptistii P. graminifolius (Pfitzer) 
P. boninensis P. odoratissimus var. 
Solla records them for: 
P. furcatus P. odoratissimus 
P. graminifolius 
P. cominsii P. pulp os us 
and in two unnamed species. 
FIGS. 8-21. Pandanus. Abaxial stomata classes 1 and 2 ( X425, except 20 and 21, which are X270) . 8, 9, 
P. pulposus. 8, Surface view; 9, transverse section. 10, P. cominsii, surface view; guard cells are among the 
shortest in the genus. 11—13, P- boninensis, different types of stomata from same area of single leaf. 14, 15, 
P. odoratissimus, different types of stomata from same area of a single leaf. 16—18, P. biakensis. 16, Transverse 
section; 17, surface view; 18, longitudinal section. 19-21, P. rockii. 19, Transverse section; 20, 21, arrange- 
ment of hypodermal cells around substomatal chambers; 20, outermost hypodermal layer; 21, next innermost 
layer. 
