Copeland . — The Mechanism of Stomata. 347 
the Gymnosperm stoma is inclined perhaps 45 0 . The plan of 
Medeola presented by a stoma whose activity is restricted 
to the ends of the guard- cells will evidently permit no great 
motility. I have found it fully worked out, so that the 
greatest diameter of the thin-walled end is quite horizontal, 
only in Osmunda Claytoniana , L. (Figs. 31-33), and O. regalis , 
L. Stahl ( 1 . c. 1894 , p. 123), from his cobalt test, decided that 
the stoma of O . regalis was non-motile ; but, while the pore 
does not close, its width varies somewhat. What movement 
occurs is an increase in the depth of the cell, in which, 
judging from the sections, the ends must be the active part. 
In the stomata which have now been described I have 
intended to include a sufficient number of forms so that the 
various mechanical devices by which the width of the pore is 
made subject to the turgescence of the guard-cells should be 
illustrated by individual stomata, which it is convenient to 
call types : and also to make clear the relation of these types. 
As is to be expected, there are complete series of intermediate 
forms connecting all these types — a limit to the profitable 
description of which might easily be reached. There are, 
however, a number of individual peculiarities, as of the stoma 
of Equisetum , which have so far been passed over only for 
the sake of consecutiveness in types. The ecological grounds 
for the development of the different types can be estimated, 
except a priori, only by ascertaining in a considerable number 
of instances what types occur under various environments. 
It will also be of some interest to see to what extent any 
relation can be traced between the taxonomic position of 
plants and the mechanism of their stomata. 
The Mosses, so far as they have motile stomata, seem 
generally to rely on an increase in the depth of the guard- 
cells to open the pore, agreeing in mechanism with Mniutn or 
Funaria , more often the latter. They have been best studied 
by Haberlandt ( 1886 ) and Biinger 1 , in whose work there is 
nothing to criticize, unless it be that Haberlandt did not seem 
1 Biinger, Beitrage zur Anatomie der Laubmooskapsel, Bot. Centralbl. xlii (1890) : 
193, 225, 257, 289, 321, 352. 
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