ALTERNATION OF GENERATIONS 151 



is a true indication of its derivative origin. In that case 

 the sporophyte may have originated from a post-sexual 

 production of spores, and have been originally without 

 vegetative tissue : the latter being produced in the first 

 instance by steriUsation of some of the potential spore 

 mother cells. Comparison among the sporogonia of 

 Liverworts and Mosses makes it appear probable that 

 such sterilisation has actually occurred in them. On 

 this theory the simple sporogonium of Riccia, which has 

 no distinction of apex and base, would represent a primitive 

 state, and more elaborate capsules may be seriated 

 progressively in relation to it. A good case can be 

 made out for an alternative view : that the Archegoniatae 

 sprang from some Algal ancestry which already possessed 

 alternate but separate generations, of which the sporophyte 

 developed from a freely shed ovum. That, on adopting 

 a land habit, the ovum, ancestrally fertihsed as it lay 

 free in the water, was retained in the parent gametophyte, 

 in a protective organ, the archegonium ; and that the 

 encapsulation had its effect in moulding and modifying 

 the young sporophyte to such forms as are seen in the 

 simplest Bryophytes. In the present state of actual 

 knowledge such suggestions are little better than 

 speculations." 



(2) To settle the precise point of origin of the Pterido- 

 phytic line with its independent sporophyte was an even 

 more difficult problem. If we elect to follow Bower's 

 original interpolation theory it is manifest that it is 

 amongst the Hepaticae, if anywhere among existing 

 forms, that we must look for this starting point, and if 

 we consider such a type as Anthoceros it does not seem 

 outside the bounds of imagination to conceive of the 

 sporocarp, already fairly highly organised, as striking 

 root for itself into the soil through the ventral layers of 

 the gametophyte. In the sporocarp of Anthoceros there 

 are all the possibihties of development of the sporophyte, 

 for it possesses a meristem, stomata, and photosynthetic 



