46 
PACIFIC SCIENCE, VoL XIX, January 1965 
The stomata in P. boninensis and P. gramini- 
folius are somewhat transitional to the next 
category. 
In all subsequent stomatal classes, papillae on 
lateral subsidiary cells are developed in exactly 
the same way, together with other kinds of pa- 
pillae on other cells. However, the former kind 
of papillae always remains simple, regardless of 
elaboration in the latter kind of papillae. Their 
only variation is in height, taller papillae being 
up to 25 fi high, as in P. aurantiacus. 
Class 3: Papillose terminal and lateral sub- 
sidiary cells (Figs. 16-18). The slight tendency 
in Class 2 stomata for the terminal to protrude 
over the lateral subsidiary cells is much more 
pronounced in Class 3. This is associated with a 
tendency for the guard and lateral subsidiary 
cells to be sunken within the epidermis. Each of 
the terminal subsidiary cells then has a promi- 
nent papilla which overarches the stomatal pore. 
Frequently papillae from opposite poles meet 
and overlap, their ends being mutually displaced 
(Fig. 17), or the papillae may even fork to pro- 
duce short interdigitating branches. Such papil- 
lae are usually adpressed closely to the stomatal 
pore, between the opposite files of papillae born 
by lateral subsidiary cells (Fig. 18). Species 
within this category include: 
P. biakensis P. copelandii P. f meatus 
Pandanus biakensis approaches the following 
type ' 
Class 4: Papillose neighboming and subsid- 
iary cells (Figs. 22-33). An advance on Class 3 
is represented by the development of papillae 
which protrude from neighbouring epidermal 
cells. This augments the outer stomatal cavity 
produced by sinking of the stomatal apparatus in 
the epidermis. The relation between papillae 
associated with stomata and those elsewhere on 
the epidermis is discussed later. Class 4 stomata 
are very diverse because the size and frequency 
of this new kind of papilla varies considerably. 
In the less elaborate types papillae are not pro- 
nounced, as in P. douglassii (Figs. 22-24), so 
that the outer chamber is shallow, but in more 
elaborate types the papillae are very tall and 
form a distinct "stockade” surrounding a very 
deep outer chamber, as in P. utilis (Figs. 28-30). 
Tall papillae further show a marked tendency to 
overarch and occlude the outer chamber (e.g., 
P. parkins onii, Figs. 25-27). 
Papillae themselves are diverse. They may 
form as a result of protrusion of the whole outer 
wall of the epidermal cell, or involve only part 
of the outer wall. Less commonly, several papil- 
lae may arise from each epidermal cell, as in 
P. patina (Fig. 32). Finally, the more elaborate 
members of this class show a tendency for the | 
papillae surrounding the stomata to become j 
lobed or shortly branched. Usually this is no- ! 
ticeable first in the terminal subsidiary cells, as 
in P. utilis (Fig. 30), and in this way a transi- 
tion to Class 5 occurs. In P. candelabrum the 
papillae are very low but often distinctly lobed. 
The following species have been included in 
Class 4, although it is clear from Figures 22-30 
that the assemblage is heterogeneous: 
P. aimiriikensis 
P. candelabrum 
P. douglassii 
P. heterocarpus 
P. micro carpus 
P. nemoralis 
P. parkinsonii 
P. patina 
P. pistillatus 
P. utilis 
P. whitmeeanus 
Sofia records elaborate stomata in the follow- 
ing species, without making distinction between 
classes 4 and 5 in the way I have done: 
P. caricosus P. silvestris 
P. helicopus P. tenuifolius 
P. micro carpus P. utilis 
P. odoratissimus 
and in 13 unnamed species. 
Class 3: Overarching papillae lobed or den- 
dritic (Figs. 34-45). This class includes the 
most specialized forms. Sinking of the stomata 
is pronounced, the deep outer stomatal chamber 
so formed being partly or wholly occluded by the 
branched papillae of terminal subsidiary and 
neighbouring cells. In the least elaborate mem- 
bers papillae are short and little lobed, as in P. 
Figs. 22—33. Pandanus abaxial stomata of classes 3 and 4. 22—24, P. douglassii. 22, Transverse section; 23, 
surface view; 24, longitudinal section. 25-27, P. parkinsonii. 25, Transverse section; 26, surface view; 27, 
longitudinal section. 28-30, P. utilis. 28, Transverse section; 29, surface view; 30, longitudinal section. 31-33, 
P. patina. 31, Transverse section; 32, surface view; 33, longitudinal section. 
