ALTERNATION OF GENERATIONS. 143 



axis of the moss. But a comparison of objects of siicli 

 prima facie diversity — objects more unlike than even the 

 large Medusce, and the ovarian cysts of the Hydra, and 

 what is more, without any intermediate connecting forms — 

 ought not, I conceive, to be adopted, except on the most 

 convincing evidence. But there is no such cogency in the 

 case, if we assume that the interpolation of a derivative 

 form occurs at a later stage of the genetic cycle in ferns 

 than in mosses ; and for this view we have ample warrant, 

 in the analogy of the Animal Kingdom, where we find cor- 

 responding differences between the Cestoid and Trematode 

 Entozoa, and between these and the Polypifera ; while 

 among the latter, even nearly allied species differ in this 

 matter of the interpolation of gemmation. Such a view, I 

 submit, is a less tax on our powers of conception than to 

 regard the minute and fugitive capsule of the moss as the 

 equivalent of the perennial and towering stem of the tree 

 fern. And no less real is the contrast between the evan- 

 escent prothallium of the fern and the foliaceous axis of the 

 moss, which, humble as is its mode of gro^vth, has yet such 

 permanent vigour of vegetative power, that its pidlulations 

 may eventually come to cover a larger space than that over- 

 shadowed by many a spreading forest tree ; for the leafy 

 shoots w^hich, year after year, cover the mossy bank with 

 verdure, and send forth each its annual clusters of capsules 

 from the impregnated archegonia, are often all of them the 

 ultimate twigs or branchlets of one original moss-plant, 

 whose primary axis and its immediate ramifications have 

 long since mouldered away, and gone to form the accumula- 

 tion of soil in which the present shoots vegetate.* 



* Mr. Jenner, in some respects, supports this view, though his idea of 

 the homologies of these orders differs in some important points from that 

 here adopted. See Edin. Philos. Joiimal, April, 1856, p. 269 ; and 

 Annals of Nat. Hist., 2d Ser., xv. 245. 



See also the Translation of Radlkofers' Observations on the Function 



