MOSSES. 309 



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

 U3, 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 which 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 ; from 



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 anotner. The 



leaf-cells of the Sphagnum bog- 



moss, fig. 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 vt" differentiation" 



Mosses, like liverworts, possess 



bothantheridiaand pistillida, which 



j .1 P r. 



are engaged in the process of fruc- 

 tification. The fertilized cell be- 

 comes gradually developed into a 



] - 164. Mouth of Capsule o f 



Funaria, showing p r isiom e . 



conical body elevated 



