\'2 
walleil. Whatever motility tliese cells may bave im like tlial |)o>,sr>M-.l Uy 
OsmuHda,^' the activity hein- restii<tea to the thin-wallea en.U. which oik-u the 
pore by an increase in depth. Finally, the stoma of Diphns U almost exactly 
like that of the Comfcnr and Allium, with a ver>' oUi<iue dorsal wall uiid Ur^ge 
overlying twin subsidiary culls. 
It is obvious in regarding the occurrence of the ilifTereut liiL'tluuuca! 
types that those the movement of which involves u change of outhne 
can operate well only where the rest of the epiilcrniis is not too rigul; 
while those the movement of whieh involves no change of outline can 
operate in spite of rigid neighboring walls, and indeed are often pfoteeteJ 
by such walls from interference Avith them by the neigliboring tissues. 
These stomata (types of Medeola and minium) regulate the openness 
of the pores by changes in the depth of the guard cells, and these changes 
are effective because the stomata are broad. Tlie firm structure of epi- 
phytes therefore puts a premium on broad stomata. The ratio of average 
length to average width of the stomata of all San "Ramon epiphytes is 
1 to 0.G7 ; of terrestrial species, 1 to 0.47. 
Even apparently differentiated subsidiary cells practically never occur 
with the stomata of the Medeola and Mnium types, which are inde- 
pendent of the contiguous cells. However, in stomata the movenu^nt of 
which involves any accommodation on the part of the adjacent cells, as 
is the case in stomata of the types of Amanjllis, Dcnnatwdtia and the 
Coniferce^ specialized subsidiary cells are or are not neccssar}*, according 
to the nature of the general epidermal cells. If the latter are very large, 
as in Diplazium, and without too rigid walls, a specialization of suljsidiary 
cells seen in surface view or in section is unnecessary and does not 
occur. Subsidiary cells are without one or the other of the two prop- 
erties of the majority of epidermal cells which interfere with the 
movements of thu guard cells; that is, either the subsidiary cells contain 
less chlorophyll than the epidermal cells, or they have less rigid walls, 
or both. They contain less chlorophyll in Asp'uUum angmtainm and 
lAndsaya pulchella and none at all in any Antropliynm, in all species of 
which genus other epidermal cells contain a certain quantity. It has 
already been pointed out that wavy, anticlinal walls increase the rigidity 
of the, epidermis. An epidermis wholly wavy or wavy next the outer 
wall (as in Antropltyum) has subsidiary cells with plane w^alls in Ctjdo- 
peltls, Nephrodluni syrmaticani, Aspidinm angulatum, AMhropteris, 
Ftetis ensiformis (not always), Antrophyum latifolium., etc., and PJlotl' 
nopteris (not always). Tlnwata lieteropJtyUa has the anticlinal Avails 
which strike the backs of the guard cells very thin, while elsewhere they 
are thick. Monograma has conspicuously broad, subsidiary cells with 
the narrow stomata. DipteHs has small, angular epidermal cells rich 
17 
Copolcuul, 1, e. 347, fi*rs, :]i to :i;J. 
