THE BRYOPHYTA 



111 



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 

 latter ; it is traversed by 

 a midrib, from which it 

 thins off on 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 



FIG. 49. General view of a plant of 

 Pellia epiphylla. oo, the lobed 

 thallus, constituting the oophyte 

 generation ; sp, the fruit, con- 

 stituting the sporophyte genera- 

 tion. The fruits to the left have 

 opened ; those to the right are 

 younger and still closed. Half 

 natural size. (After Cooke.) 



