Stomatal Structure in Pandanaceae — Tomlinson 
43 
originates (Fig. 3) are somewhat larger than 
adjacent hypodermal cells, have large nuclei, but 
most conspicuously include a fine granular de- 
posit by which they may be recognized even 
before the chamber appears. Guard mother cells 
are recognizable by their position immediately 
above a chamber, but are not otherwise cyto- 
logically different from neighbouring cells of the 
stomatal file (Fig. 4). They only divide once 
after becoming recognizable, by the longitudinal 
wall which produces the guard cells, this usually 
being the last division in the development of 
the stomatal complex. Size of substomatal cham- 
ber gradually increases as the stomatal complex 
develops and is a useful indicator of the level of 
maturity of the complex ( cf Figs. 5,7). 
Transverse divisions may continue in those 
cells of the stomatal file which are not guard 
mother cells. Such divisions in cells situated at 
each pole of the guard mother cell produce the 
terminal subsidiary cells (Fig. 6). These divi- 
sions are never synchronous and may occur early 
or late, but usually are completed before the 
divisions which delimit lateral subsidiary cells. 
Cells belonging to files on each side of the guard 
mother cell produce lateral subsidiary cells. Two 
successive divisions occur at opposite ends of 
each cell, each division cutting off by an oblique 
wall a small cell which is remote from the guard 
mother cell from a much larger cell next to the 
guard mother cell ( Fig. 5 ) . Rarely divisions in 
this lateral subsidiary mother cell are longitudi- 
nal and not oblique. The last division in the 
stomatal complex is almost invariably the longi- 
tudinal division which produces the guard cells, 
although rarely divisions producing terminal 
subsidiary cells do occur later than this. 
Development of stomata does not follow a 
strict acropetal succession, and stomata at dif- 
ferent stages of development occur in a small 
area of the leaf. In general, however, divisions 
which produce terminal subsidiary cells are com- 
pleted first; divisions producing lateral sub- 
sidiary cells, which occur throughout a relatively 
wide region, are completed second; and divisions 
which produce guard cells are usually last. Divi- 
sions within a single complex are rarely syn- 
chronous, so that only one division figure per 
stoma is usually seen. 
Division in the guard-cell mother cell is as- 
sociated with further internal development. As 
soon as guard cells are produced, but before the 
stomatal pore opens, enlargement of the sub- 
stomatal chamber by separation within the sec- 
ond hypodermal layer occurs. When the stomatal 
pore opens there is thus communication with 
the internal leaf atmosphere. 
This type of stoma corresponds to neither of 
the two main types recognized by Florin (1931) 
in gymnosperms, although in most resembles the 
amphicyclic. It is neither similar to development 
described by Stebbins and Khush in Juncus and 
Sagittana, nor is it similar to that in Trade- 
scantia as these authors suggest. 
Because of the constant disposition of stomata 
in relation to the two outermost hypodermal 
layers and because of regular partitioning in 
these layers, the outer hypodermal cells which 
immediately surround the substomatal chambers 
have a very uniform shape and arrangement in 
all Pandanaceae. In the outermost layer the 
chamber represents a space between longitudinal 
walls and is enclosed by two U- or V-shaped cells 
(Fig. 20); in the next innermost layer the cham- 
ber represents a space between transverse walls 
and is surrounded by two kidney-shaped cells at 
right angles to the cells without (Fig. 21). Fur- 
ther inner hypodermal layers are not uniformly 
disposed. Variation in stomatal structure largely 
involves papillae developed on subsidiary and 
Figs. 2-7. Stomatal development in Pandanus (XI 160). 2, Diagrammatic representation of surface layers, 
showing epidermal stomatal files (stippled) in relation to hypodermal layers. 3, Arrangement of cells of outer- 
most hypodermal layer at time of initiation of substomatal chamber. 4, Corresponding arrangement of epidermal 
cells immediately above Figure 3, stomatal complex recognized largely by position. 5, Oblique division in lateral 
subsidiary mother cell. 6, Transverse division in terminal subsidiary mother cell at a time when one division 
has occurred in each lateral subsidiary mother cell. 7, Arrangement of cells in stomatal complex prior to last 
division, that of the guard mother cell. 
In Figures 4-7 the cells surrounding the guard mother cell are cross-hatched for ease of recognition. They 
are not distinguished in any obvious cytological way. Inset in Figures 5 and 7 shows size of corresponding 
substomatal chamber: s.s.c., substomatal chamber; g.m.c., guard mother cell; t.s.m., terminal subsidiary mother 
cell; l.s m., lateral subsidiary mother cell; s.l.s., sister cell of lateral subsidiary cell. 
