32 BRITISH MOSSES. 



In animals, to again quote Prof. Milnes Marshall, " re- 

 capitulation is not seen in all forms of development, but 

 only in sexual development, or at least only in development 

 from the egg. In the several forms of asexual development 

 of which budding is the most frequent and the most 

 familiar, there is no repetition of ancestral phases, neither 

 is there in cases of regeneration of lost parts." 



In Mosses, on the contrary, the table last given shows 

 that in most of the modes of reproduction the ancestral 

 form, the algoid protonema, is retained and reproduced, 

 whereas in the growth from a sexual cell, i.e. in the 

 sporogone, the ancestral form entirely disappears. 



Organization. I now propose to describe somewhat 

 more in detail certain parts of the structure of a Moss. 



The stem of Mosses is, as we have already seen, very 

 variable in size. Sometimes, as in the Phascum (Fig. 17)f 

 the whole plant is almost sessile ; in other cases, as in 

 the Polytrichum (Fig. 2), it attains to a very considerable 

 length. In some Mosses inhabiting water, the length of 

 the plant reaches to feet. In our flowering plants the 

 stem is supported by the presence of fibro-vascular 

 bundles, i.e., fibres arranged in combination with tubes 

 along which fluids can and do pass. But with the ex- 

 ception of one family, the stem of the Mosses, like all the 

 other parts of the plant, is constituted of cells alone, and 

 consequently the circulation of fluid in them appears to 

 result entirely from the passage of fluid through the walls 

 of the cells. Hence their close dependence on the presenceof 

 moisture ; hence in dry weather they fade and droop, and 

 with the return of moisture assume their wonted appearance. 



