6 TORREYA 



naturally to a comparison and homologizing of vegetatively-produced spores 

 of algae with meiospores, though the two are fundamentally and entirely un- 

 like in their significance in the reproductive life cycle. This has been referred 

 to earlier in the present paper. 



Thirdly, the consideration of reproduction by spores produced by meiosis 

 as a strictly asexual process in contrast to sexual reproduction by the fusion 

 of gametes has tended to dissociate the two cytogically important processes in 

 the life cycle ; — syngamy and meiosis. Too often in elementary (and advanced) 

 texts the reduction in chromosome number which occurs at meiosis is con- 

 sidered as occurring during a division which is contrasted with an ordinary 

 cell division (mitosis). It is generally recognized that the reduction in chromo- 

 some number occurs during a series of two divisions ; that the term, a reduc- 

 tion division, is decidedly a misnomer. It is well known, even by those who are 

 responsible for statements in textbooks such as " — in reduction division — the 

 chromosomes do not split at all — ". that the chromosomes do split during the 

 first meiotic division. But this is done in an attempt to contrast "reduction 

 division" with mitosis, since " — in ordinary cell division the chromosomes split 

 longitudinallv — ." Xow the reduction in chromosome number is not a process 

 to be contrasted with mitosis, since it itself may be considered as consisting of 

 two mitoses (Sharp. 1934. Chap. 16). but is a process to be contrasted with 

 svngamv. Meiosis is not simply a type of cell division but represents the cul- 

 mination of the sexual process which is initiated by the fusion of gametes. The 

 process of syngamy introduces the two sets of chromosomes into one nucleus. 

 The final association of the chromosomes during which there occurs not only 

 an intimate association (synapsis) but even an interchange of parts (chiasmata 

 formation; crossing over) takes place during meiosis, the culminating feature 

 of sexual reproduction. The sporophytic generation is an interlude in the sex- 

 ual process. The sporophyte is a sexual generation. The meiotic production of 

 spores and the growth of a new individual from each, is part of the process of 

 sexual reproduction. 



In advanced texts dealing with the groups of plants, the viewpoints are 

 variable. Fritsch (1935) distinguishes between the significance of zoospores 

 from the haploid plant and those from the zygote, since in discussing the life 

 cycles of Algae he says. " — in addition to reproducing by sexual means it 

 (the gametophytej may also exhibit abundant asexual reproduction. This 

 latter is. however, actually an accesory means of reproduction and, in relation 

 to the general course of the life cycle, has not the same significance as the forma- 

 tion of asexual swarmers or other reproductive cells from the zygote which 

 ensues after the occurrence of meiosis." (p. 51). The distinction is not clearlv 

 followed, however, since the production of asexual spores (zoospores, aplano- 

 spores. etc. ) by the gametophyte and the production of spores from the zygote 

 by meiosis are both considered under the discussion of asexual reproduction and 



