MOSSES. 



309 



winter's cold. The common, or Wall Screw-moss, fig. 

 163, growing almost every where on old walls and other 

 brick- work, if examined closely, will be found to have 

 springing from its base numerous very slender stems, each 



Fig. 163. Screw Moss. 



of wh.ch terminates in a dark brown case, which encloses 

 its fruit. If a patch of the moss is gathered when in 

 this state, and the green part of the base is put into water, 

 the threads of the fringe will uncoil and disentangle them- 

 selves in a most curious and beautiful manner ; frcm 

 this circumstance the plant takes its popular name of 

 Screw-moss. The leaf usually consists of either a single or 

 a double layer of cells, having flattened sides, by which 

 they adhere one to another. The 

 leaf-cells of the Sphagnum bog- 

 moss, tig. 179, exhibit a very curi- 

 ous departure from the ordinary 

 type ; for instead of being small and 

 polygonal, they are large and elon- 

 gated, and contain spiral fibres 

 loosely coiled in their interior. Mr. 

 Huxley pointed out, that the young 

 leaf does not differ from the older, 

 and that both are evolved by a 

 gradual process of" differentiation" 

 Mosses, like liverworts, possess 

 bothantheridiaand pistillida, which 

 are engaged in the process of fruo- 

 tification. The fertilized cell b&- 

 eonies gradually developed into a conical body elevated 



