48 
PACIFIC SCIENCE, Vol. XIX, January 1965 
capitellatus, which is thus intermediate between 
classes 4 and 5 (Figs. 34-36). Increasing elab- 
oration can be seen in a number of species 
whereby the papillae become taller, elaborately 
lobed distally, the lobes tending to interdigitate 
and form an incomplete canopy above the outer 
stomatal chamber (Figs. 40-45). The ultimate 
condition, and the most elaborate stomatal type 
in Pandanus, was observed in an unidentified 
species cultivated in Florida in which the canopy 
was so complete that the guard cells were com- 
pletely obscured from surface view, a somewhat 
more elaborate condition than that illustrated in 
Figure 44. 
As in previous classes the papillae arising 
from terminal subsidiary cells may be either 
erect or adpressed to the pore ( Fig. 42 ) , a fea- 
ture constant for each species. Where these 
papillae are adpressed, and indeed to a certain 
extent in other examples, the outer chamber is 
partially occluded by papillae which are ele- 
vated to three different levels: papillae from the 
lateral subsidiary cells being shortest, from the 
terminal subsidiary cells being intermediate, and 
from the neighbouring cells being tallest (Figs. 
40, 43). Clearly, in these most elaborate types 
water vapour must pass through quite a laby- 
rinth on its way through the epidermis. Species 
of this category include: 
P. archboldianus P. erinaceus 
P. aurantiacus P. nigridens 
P. capitellatus P. pygmaeus 
( b ) Freycinetia 
Freycinetia includes species with unspecialized 
stomata, corresponding to Class 1 above, and 
where stomatal elaboration does occur it seems 
to follow a different trend to that in Pandanus, 
although insufficient material has been examined 
to be certain of this point. Specialization in 
Freycinetia involves sunken stomata, overarched 
by simple papillae from terminal and neighbour- 
ing cells only. Papillae are never lobed. Rows of 
papillae on lateral subsidiary cells which are so 
characteristic of stomata in classes 2-5 in Pan- 
danus have never been observed in Freycinetia, 
except by Solla in one unnamed species (which 
might be a Pandanus misidentified ) . Further 
observation is needed to discover if there is a 
constant difference between Pandanus and Frey- 
cinetia in this respect. Figures 46-48 represent 
the most elaborate condition seen by me in 
Freycinetia. 
The following species, together with six un- 
named species listed by Solla, have unspecialized 
stomata: 
F. banksii F. lucens 
F. excelsa F. mariannensis 
F. javanica 
The following has specialized stomata: 
F. arborea 
Solla records specialized stomata in three un- 
named species. 
Further peculiarities of epidermal structure in 
Freycinetia are mentioned below. 
VARIATION IN STOMATAL STRUCTURE 
The above account gives an impression of the 
range of stomatal structure throughout the Pan- 
danaceae and, at least for Pandanus, demon- 
strates a linear series of increasingly specialized 
types, each arbitrary class which has been dis- 
tinguished being more specialized than the pre- 
ceding. This trend seems to be unidirectional, as 
can be understood when the stomatal variation 
in a single individual is considered. A number of 
ancillary observations need to be outlined first. 
(i) Occluded stomata. Frequently stomata 
were observed which stain intensively with sa- 
franin, in contrast to normal stomata. These 
evidently correspond to the "lignified” stomata 
of Kofler (1918). Such stomata become oc- 
cluded by resinous or tanniniferous material 
which plugs the stomatal pore. Subsequently the 
guard cells die and their back walls collapse 
against the front walls. Usually the substomatal 
FIGS. 34-45. Pandanus abaxial stomata of classes 4 and 5 (except 39, which shows an adaxial stoma). 
34-36, P. capitellatus. 34, Transverse section; 35, surface view; 36, longitudinal section. 37, 38, P. pygmaeus. 
37, Transverse section; 38, surface view. 39-42, P. archboldianus. 39, Adaxial stoma, surface view; 40, trans- 
verse section; 41, surface view; 42, longitudinal section. 4 3-4 5, P. nigridens. 43, Transverse section; 44, surface 
view; 45, longitudinal section. 
