WAHL: ALTERNATION OF GENERATIONS 9 



here concerned, however, only with those reproductive terms constantly used 

 in an elementary presentation. We have already called attention to the con- 

 fusion that may result when the term asexual reproduction is used in connec- 

 tion with vegetative reproductive processes and with the production of meio- 

 spores. Since the latter is part of sexual reproduction, since the term vegeta- 

 tive reproduction adequately describes the former and since asexual reproduc- 

 tion has been used to denote entirely different processes, it would seem best to 

 discontinue use of the term asexual reproduction entirely. This, as before 

 mentioned, has been done in one recent text. Tilden (1935) uses the term 

 spore only for meiospores and the term gonidium for vegetatively produced 

 spores. It seems more expedient to the author to continue the use of the term 

 spore for both of these categories, simply recognizing that meiospores (includ- 

 ing ascospores and basidiospores) are sexual spores while other kinds of 

 spores are vegetatively produced. Spores, then, are usually one-celled repro- 

 ductive bodies which produce new plants by direct growth, in contrast to 

 gametes which are one-celled reproductive bodies which fuse together. For the 

 purpose of teaching Elementary Botany it is unfortunate that there exist in 

 the plant kingdom such a multiplicity of kinds of spores. The facts make 

 necessary the application of numerous prefixes to describe certain types of 

 spores such as zoospores, conidiospores, uredospores, meiospores, etc., etc. The 

 problem is not simplified by failing to recognize that some of these are vegeta- 

 tively produced while others are involved in the sexual reproductive pro- 

 cesses. 



We may now comment briefly concerning the bearing of the ideas pre- 

 sented in this paper on the relative merits of the antithetic and homologous 

 theories of alternation of generations. Fritsch has been one of the leading propo- 

 nents of the idea that the origin of the alternating generations, at least as they 

 occur in members of the Pteridophyta, is to be sought in the type of algal plant 

 body which occurs in certain members of the Chaetophorales of the Green 

 Algae. Members of this group exhibit the heterotrichous type of plant body 

 which consists of a prostrate creeping system, often more or less pseudoparen- 

 chymatous, and a more or less, upright system of usually branching filaments. 

 In some cases (e.g., Trentepholia) zoospore production is confined to the up- 

 right system and gamete production to the prostrate system. 



According to Fritsch (1916, p. 240) this condition provides "all the neces- 

 sary indications for the gradual differentiation of two alternating generations, 

 of which one bears the asexual organs on the upright system, the other bears 

 the sexual organs on the creeping base. Disappearance of the base in the 

 former, and of the upright system in the latter — will give two different genera- 

 tions, resembling those of the Archegoniatae in all respects." This is inciden- 

 tally referred to again in a later paper (1920, p. 170). "An alternation be- 

 tween sexual and asexual phases must have come about as soon as the reduc- 



