STOMATA, 239 
which establish a direct connection of the intercellular spaces of 
the inner tissue with the atmosphere. Besides on leaves, 
stomata are also found on seed-vessels, young axial organs (stems), 
and even on the walls of the ovary, but never on roots. 
On leaves the stomata occur for the most part only on the 
lower surface (Figs. 127, 129), or the latter is at least more 
abundantly provided with them than the upper surface. This 
applies, however, only to bifacial leaves, the centric leaves (see 
page 210) having stomata on both sides (Fig. 128). In the 
monocotyledons the stomata lie mostly in straight lines, the 
cleft having the same direction in all (Fig. 156); in the dicoty- 
ledons they are irregularly distributed (Fig. 154). 
Fig. 155.—Vertical section of a stoma from a leaf of Mentha piperita; Ep, norris 
¢, Cuticle; mer, leaf merenchyma; 8, guardian cells; E, eisodial opening; 0, opisthia 
opening; A, respiratory cavity; n, lateral cells (Tschirch). 
Their form and development ’ is very varied. Plants occur- 
ring in dry climates have variously protected (depressed) stomata 
(Figs. 63, 128). 
There are distinguished on the stoma (Fig. 155) the guard- 
ian cells (s), the central cleft (porus), and the eisodial (Z#), and 
opisthial opening? (0). Beneath the guardian cells there is 
. i i im’s Jahrbiicher f. wissensch. Botanik, iv., 1862, P. 
Nigh Praedaisa Ibid., v., plates 34-36. Tschirch, “ Ueber ma 
Beziehungen des anatom. Baues der Assimilationsorgane zu Klima sige 
Standort,” Linnea, 1881. In the latter the entire literature relating 
the stomata is given up to the year 1881. 
* Compare Tschirch, loc, cit., p, 140. 
