238 THE SIMPLEST LAND PLANTS 



(Fig. 37, D, el.). A large bunch of them arises from 

 the base of the capsule. The elaters are very hygro- 

 scopic, i.e. very sensitive to small changes in the 

 amount of water vapour in the air, and as they take 

 up or lose water from the air they twist about, dis- 

 turbing and scattering the mass of spores, which float 

 of£ into the air. 



The spores are large and multicellular (Fig. 37, D, 

 spo.), i.e. the original spore cell divides into several 

 cells on ripening, and these contain chloroplasts. The 

 spores do not form a resting stage in the life history, 

 they die unless they quickly fall upon damp soil where 

 they can germinate. One of the cells grows out and 

 gives rise to the apical cell of the new Pellia plant, 

 and the first rhizoids grow from the ends of the spore. 



Besides the thalloid forms, of which Pellia is one, 

 there are many Liverworts whose shoots have distinct 

 stems and leaves, the leaf being a thin membranous 

 structure consisting of a single layer of cells containing 

 chloroplasts. The cells of the stem are longer and 

 often thick-walled, but there is very little tissue 

 differentiation. These leafy Liverworts live largely on 

 rocks or tree-trunks in wet climates, and absorb water 

 through the whole surface of the plant, especially 

 the leaves. They are attached by rhizoids to the 

 substratum on which they grow, but the rhizoids are 

 of no importance in the absorption of water, as those 

 of Pellia are. 



Mosses. — The Mosses always have their shoots differ- 

 entiated into stem and leaf, and most of them have 

 a certain amount of tissue differentiation, considerably 

 more than the Liverworts. They are on the whole 

 larger plants than the Liverworts, and depend more 

 upon absorption of water from the soil, though a 



