241 



It may at this juncture be useful to consider what must have 

 been the general result of the initiation of conjugation between uni- 

 cellular organisms in past ages. When conjugation between pairs of 

 similar cells arose among the primeval Protozoa (or Protophyta) the 

 original form of this process was bound to result in the "creation" 

 of two different generations. These were characterised primarily by 

 a difference in the number of chromosomes. The one generation with 

 double chromosomes was itself never capable of conjugation, it could 

 only give rise to new forms by fission, and it, or its progeny so pro- 

 duced, could only bring about a new conjugation by first producing 

 (spore-formation) a generation in which the number of chromosomes 

 was reduced in each individual product to the original one, which 

 obtained antecedent to a conjugation. 



Notwithstanding all those facts of Protozoan modes ^) of repro- 

 duction which may appear to tell against this, notwithstanding all the 

 botanists believe about the secondary nature of alternation of genera- 

 tions, it must be insisted that a simple antithetic alternation of gene- 

 rations was obligatory from the very nature of the original conju- 

 gation. 



All subsequent higher developments must be considered as effected 

 by further specialisations on the original "plan". 



The Protozoan stage might be improved upon by the one gene- 

 ration or the other, or by both. The conjugating generation may 

 have become Metazoan, or the spore-producing one, or both together 

 may have undergone the higher evolution ^). It is probable that there 

 were originally variations here, and some of these may still persist. 

 In plants the amplification of the zygote stage has given rise to the 

 sporophyte, which is sharply separated from the sexual generation 

 or gametophyte by a one-celled stage (the spore) and a reducing 

 division. The whole of the cells of the gametophyte must be looked 

 upon as morphologically aequivalent, some becoming differentiated as 

 vegetative organs by sterility, others retaining the primitive character 

 of becoming conjugating gametes. Bower ^) has attempted with some 

 success to derive the members of the sporophyte by a similar sterili- 

 sation of sporogenous tissue. The standpoint here taken up is, in 



1) In the sequel an attempt will be made to show, by concrete 

 instances which have beeu thoroughly investigated by other observers, 

 that many of these are secondary in nature. 



2) This must be held as true for the plant kingdom also. 



3) F. 0. Bower, Studies in the Morphology of Spore -producing 

 Members. Phil. Trans., 1894. B, 



16 



