WAHL: ALTERNATION OF GENERATIONS 7 



no mention is made of the latter in what is here considered their proper rela- 

 tion, that is, as part of the sexual process. The sporophyte is considered an 

 asexual generation and the production of meiospores is considered an asexual 

 process. In fact, in a previous paragraph (p. 41) the statement is made that 

 "Of a comparable nature to aplanospores are the endospores formed in certain 

 Myxophyceae and the tetraspores of Rhodophyceae and Dictyotales." This may 

 be meant to refer only to their method of formation, however, and not to their 

 significance in the life cycle. 



Although Fritsch's book is not intended for use in elementary courses in 

 general botany, the above quotations serve to emphasize the difficulties that 

 arise with beginning students when a life cycle is considered as consisting of an 

 alternation between a sexual and an asexual phase in which the sexual phase 

 may also reproduce asexual ly, and in which the asexual phase may also re- 

 produce by other asexual or vegetative methods which have not the same 

 significance as its "normal" method of reproduction. How much simpler, and 

 more correct, to consider the sexual life cycle as including syngamy and meio- 

 sis, with the interpolation of growth phases, either or both of which may have 

 vegetative (asexual) methods of reproduction. 



Smith (1933, 1938a), in his treatments of the Algae, generally considers 

 the meiotic production of spores under the heading of asexual reproduction, 

 except where meiosis shortly precedes syngamy, as in Fucus, in which case it 

 is part of the sexual process. He does, however, distinguish, in some brown 

 algae, between meiospores and vegetative spores, designating the latter as 

 "neutral" spores since they produce the same type of plant from which they 

 originate. In the case of Fucus, it seems at least as logical to consider the plant 

 a gametophyte in which meiosis has been delayed until the production of 

 gametes, the sporophytic generation having been eliminated or never produced, 

 as to consider a plant that produces cells which function as gametes a sporo- 

 phyte because the cells of the plant are diploid. 



In his treatment of the bryophytes and pteridophytes, Smith (1938b) 

 definitely considers the gametophyte a sexual generation and the sporophyte 

 an asexual generation, although he describes the gametophytes as also repro- 

 ducing asexually by gemmae and by other vegetative methods. The same view- 

 point is expressed by Campbell (1918) in his "Mosses and Ferns." 



Tilden (1935), on the other hand, considers the alternation of generations 

 as an alternation between sexual generations. "Sexual reproduction .in the plant 

 and animal kingdom includes, or has to do with, the entire normal life cycle, 

 consisting of a morphological or cytological alternation of haploid and diploid 

 generations. The sporophyte is as much a sexual organism as is the gameto- 

 phyte, since it carries in its body the sex-bearing chromosomes" (p. 236). She 

 restricts the use of the term spore to reproductive cells which are the products 

 of meiosis, and this process is considered part of sexual reproduction. "Sexual 



