420 
Delf . — Transpiration in Succulent Plants . 
seriously the water content of the epidermal and guard cells. It will be 
seen that a change in dimensions of the rift of 20 per cent, was accompanied 
by a change of 28 per cent, in the rate of transpiration ; it is suggested that 
the two processes are therefore closely connected. 
Table IV. 
Transpiration and Behaviour of Stomata in Salicornia amnia. 
J oss in Weight due to Transpiration. 
Time. Light. Water Loss. 
11.35 a - m - 
12.35 p.m. 11 0-0194 gm. 
2.35 p.m. 50 0-0140 gm. 
Diminution in rate of Transpiration = 
28 % 
Average size of Stomata. 
Guard Cells. Rift. 
Length. Diameter. Length. Diameter. 
9.5 7.2 5.1 1.9 
7.7 6.9 4.1 1.4 
Diminution per cent. = 
6 7.7 20 20 
As has already been stated, the stomata of xerophytic succulent plants 
are commonly depressed below the level of the epidermal cells. In many 
cases they are further protected by wax, as in Euphorbia Tirukallil where 
a ring-like wall of wax surrounds each stoma ; by cuticular projections 
overarching the guard cells, as in the case of Aristida ciliata described 
by Volkens ; or by subsidiary cells, as in the stomata of some of the 
Bromeliaceae recently described by Linsbauer, to which reference has 
already been made. 
The stomata of epiphytes are, however, often not at all sunken or 
protected, as in the epiphytes described by Holtermann 2 from damp, 
shaded spots in the Ceylon forests. The stomata of Rhizophora , Bruguiera , 
Aegeciras , and other Mangroves were stated by Schimper 3 to be sunken, 
but in nearly every case examined by Holtermann this was not found to be 
the case. In many species of Atriplex the stomata lie below chinks in the 
parenchymatous covering of leaves, but are not at all depressed below the 
level of the epidermal cells. In all the species of Sedum and in all the 
succulent halophytes (excepting two species of Suaeda) which I have 
observed, the guard cells are not at all sunken. 
In many cases, especially in the leaves of tropical epiphytes, the 
transpiring surface is supplied by aqueous tissue interposed between itself 
and the assimilating cells. The aqueous tissue consists of colourless, 
usually parenchymatous cells filled with a watery cell-sap, which is often 
readily given up, both in transpiration and in supplying the assimilating 
tissue. As the cells of the aqueous tissue are gradually depleted of their 
water, the thin walls collapse, and the collapsed cells form a more or less 
complete protection to the cells of the mesophyll. When a further water 
1 Haberlandt, Dr. G. : Physiologische Pflanzen-Anatomie, 1896, p. 397. 
2 Holtermann, Dr. C. : Der Einfluss des Klimas auf den Ban der Pflanzengewebe, 1907. 
3 Schimper, A. F. \V. : Die indomalayische Strandflora, 1891. 
