306 TIJAXSACTIONS AND PKOCEEDINGS OF THE [sess. i.xtv. 



fertilisation which would otherwise lead to the indefinite 

 increase of tlie number of chromosomes by constant 

 doubling.' Hertwig (13) states that it may occur before 

 or after fertilisation, citing in example of the former the 

 condition in animal oogenesis, and of the latter, the 

 reducing division described by Ivlebahn for the germinating 

 zygotes of Desmids. 



In Fucus (a type described as without alternation of 

 generation). Farmer and Williams (14) describe the reduction 

 as occurring in the oogonium during the ripening of the 

 oospheres : on conjugation, the full number is restored 

 and is found in the vegetative plant — the gametophyte. 

 These observers point out how closely this approximates 

 to the type of animal oogenesis. 



On the analogy of certain animal types, as outlined 

 by Beard and Murray (15), the existence in Fucus might 

 be suspected of a degenerate sporophyte as the product 

 of germination of the oospore on which the gametophyte 

 would arise aposporously, while the reduction is postponed 

 to the latest minute. 



This in turn suggests the possibility of aposporously 

 jiroduced fern prothalli liaving the full number of 

 chromosomes like the sporophyte, and the necessary 

 nuclear reduction occurring during the maturation of 

 the ovum. 



On the other hand, seeing that the reduction occurs 

 in higher forms — certain Liverworts, Gymnospo^ms, and 

 Angios'perins (see Strasburger, loc. clt. for references) — 

 in the spore mother-cells, so that the gametophyte has 

 the half and the sporopiiyte the full number, and that its 

 appearance is apparently coincident with the development 

 of the sporogenous tissue, the change of position in the 

 life cycle may be of the nature of a " time-displacement." 



On this point it would l)e interesting to have information 

 as to where the nuclear reduction occurs in such forms as 

 Hkc.ia and (Joh'odtcrte, which exhiljit the most primitive type 

 of sporophyte; whether, for example, the spores of CohoclKcte 

 liave the half number, and consequently the gametophyte 

 also; or if the reduction occurs at the same point as in 

 Fucus, and the gametophyte has the full number; similarly 

 in regard to Uhxia, whether the sporogonial envelope, as 



