574 MOSSES AND FERNS chap. 



that the weight of evidence is very much in favour of the 

 antithetic theory of the ahernation of generations, and that 

 there is a real genetic connection between Bryophytes and 

 Pteridophytes. The sporophyte of the latter is directly 

 descended from some bryophytic ancestral form, although it 

 is quite probable that the existing Pteridophytes may have 

 been derived from more than one ancestral type. All of the 

 Archegoniates agree closely in their most important structural 

 details. The sexual organs and method of fertilisation, and the 

 early divisions of the embryo, are very much alike in all of 

 them. There is evident in all of the higher Bryophytes a tend- 

 ency to a subordination of the sporogenous function to the 

 vegetative existence of the sporophyte, with the development of 

 conducting and assimilating tissues comparable to those in the 

 sporophyte of the vascular plants. Finally, the spores produced 

 by the sporophyte are identical in structure in the two series of 

 archegoniate plants. 



The really weighty argument on the other side is the occur- 

 rence of apogamy and apospory. As to the significance of 

 these phenomena, they may probably be compared to the adven- 

 titious budding, so common in many of the higher plants. In 

 both Pteridophytes and Spermatophytes, the whole sporophyte 

 may arise by budding from almost any portion of the plant- 

 body. Thus in Camptosorns or Cystopferis hulhifera, the 

 young sporophyte arises from the leaf, as it does in Begonia or 

 Bryophylhim among the Spermatophytes. In Ophioglossum it 

 may arise from the root-apex, a condition paralleled among the 

 Spermatophytes by the production of root-buds or suckers in 

 Popiilus or Anemone. Certain supposed cases of parthen- 

 ogenesis in the Spermatophytes have been shown to be rather 

 cases of budding from the nucellar (sporangial) tissue, and 

 many other instances could be cited showing similar conditions. 



No morphologist has ever regarded such adventitious origin 

 of the sporophyte as indicating in any sense of the word a rever- 

 sion to a primitive condition. It is not argued that because the 

 sporophyte may arise as a bud from a root, that therefore the 

 sporophyte originated first as a modification of a root. In the 

 same way, it does not seem reasonable to argue from the doubt- 

 fully norm.al phenomenon of apogamy that the sporophyte 

 developed in the first place as a vegetative modification of the 

 gametophyte. 



