BRYOPHYTA. 101 



A microscopical examination of the leaves, which are quite destitute of 

 a midrib, shows them to be composed of a network of narrow chlorophyll- 

 bearing cells surrounding much larger empty ones whose walls are marked 

 with transverse thickenings, and perforated here and there with large, 

 round holes (Fig. 64, (7). It is to the presence of these empty cells that 

 the plant owes its peculiar spongy texture, the growing plants being fairly 

 saturated with water. 



The Andreceacece are very small, and not at all common. The 

 capsule splits into four valves, something like a liverwort. 



The Phascacece are small mosses growing on the ground or 

 low down on the trunks of trees, etc. They differ principally 

 from the common mosses in having the capsule open irregu- 

 larly and not by a lid. The commonest forms belong to the 

 genus Phascum (Fig. 65, A). 



The vast majority of the mosses the student is likely to 

 meet with belong to the last order, and agree in the main with 

 the one described. Some of the commoner forms are shown 

 in Figure 65. 



