THE BE-YOPHYTA 



111 



00. 



of brooks or wells, or in damp woods and hedgerows, 

 sometimes actually living under water ; in other cases, 

 however, it grows on comparatively dry sandy ground. 

 The plant in its vegetative condition is a green, flat, lobed 

 thallus, repeatedly branched, the lobes often overlapping 

 each other (see Fig. 49). 



The plants grow socially, and may collectively cover 

 a considerable patch of 

 ground. If we cut off a 

 part of the thallus and 

 examine it, we find that it 

 forks repeatedly, all the 

 branches lying nearly in 

 the same plane. The 

 thallus has an upper and 

 under surface, the former 



darker green than the FlG> 49. General view of a plant of 

 latter ; it is traversed by 



. 

 a midrib, from which it 



thins Off 011 either side 

 towards the margins (Fig. 



50). On the under-side 



numerous root-hairs arise, 



which spring from the midrib and fix the plant to the 



ground ; for Pellia, like other Bryophyta, possesses no 



true roots. 



The whole character of the plant varies greatly according 

 to the conditions under which it grows ; so much so that 

 its different forms would never be supposed to belong to 

 the same species, if the transitional states had not been 

 observed. Under water (where, by the bye, Pellia never 

 fruits) the thallus is long, narrow, and strap-shaped, 

 branched at rather distant intervals, with a very distinct 



Pdlia epiphyiia. oo, the lobed 



thallus, constituting the oophyte 

 generation ; sp, the fruit, con- 

 ^tltuting the sporophyte genera- 

 tion. Ihe iruits to the left have 

 opened ; those to the right are 



7&* and ^ c /, os f , Hal * 



natural size. (After Cooke.) 



