638^ 



How otherwise could the gametophyte come into existence as a 

 distinct morphological entity V 



Prof. Mac Millan, as before stated, cites certain jjlants in dis- 

 proof of the view of the origin of the gametophyte by sterilization, 

 and of these instances we may note the one, Sphaeroplea, to 

 which attention is specially called by our critic. Here the so-called 

 "vegetative" cells are all potentially capable of forming gametes, some 

 "oospheres" (why not call them ova?) others spermatozoids. Thus, 

 as all the cells are potentially reproductive cells, it is, in our humble 

 opinion, incorrect to term them vegetative. There is no division of 

 labour, and no cells are specially set apart to nourish the colony or 

 community, that function, and the reproductive one also, being per- 

 formed by every cell alike. In other words, and again regarding 

 Sphaeroplea, it may be noted that our statement to the effect 

 that "the whole of the cells of the gametophyte must be looked upon 

 as morphologically equivalent", is here borne out by the facts, for all 

 the cells are endowed with the same morphological potentialities. But 

 it must not be overlooked that here we have the merest indication 

 of a gametophyte, or, to use the words of Bower regarding the 

 sporophyte of this and other Algae with reference to a game- 

 tophyte, we can say that its existence is "barely sketched out"^). 



Prof. Mac Millan is, furthermore, interested 2) to know what 

 explanation would be given of the life-histories of those plants which 

 have a direct segmentation of the syngamete or zygote without any 

 antithetic alternation whatever. As examples he cited F u c u s , 

 Vaucheria, and Spirogyra. 



It will be time enough to throw these at us when our critic, or 

 some one else, shall have thoroughly worked out all the details of 

 their life-histories, more especially the nuclear changes and the evi- 

 dences of the presence or otherwise of a reduction of the number 

 of chromosomes at some point or other in the life-history. 



Assuming, with Boveri and Strasburger, the chromosomes to 

 be entities which retain their individuality, — and this is the as- 

 sumption on which ray argument regarding the lower forms of life 

 is based, — after every conjugation and antecedent to a new one a 

 reduction in the number of chromosomes is absolutely necessary. 

 There is no getting over the fact of the duplication at conjugation, 

 and, however much dispute there may be as to the mode or modes 



1) Bower, 1. c. yj. 486. 



2) p. 440—441. 



