SEXUAL REPRODUCTIOX IN ALGJE 531 



the average larger than sexual plants" a condition which 

 is true of a number of species of the Rhodophyceae with 

 which the writer has had a rather extensive field ac- 

 quaintance. This is a point of sonic importance, since too 

 great emphasis may be placed on the resemblance in form 

 between the two generations (a resemblance which seems 

 most natural since the plants develop under closely sim- 

 ilar life conditions), and important differences in size, 

 dimensions of the cells, and general vegetative vigor 

 may not receive the attention that they deserve. If the 

 fusion of gamete nuclei is to be regarded as the stimulus 

 to a sporophytic generation, the period of chromosome 

 reduction is equally characteristic of its end, and the sec- 

 ond event follows as a natural consequence upon the first. 

 Mitoses with the diploid number of chromosomes when- 

 ever they occur between these two events furnish, in the 

 opinion of the writer, the only safe criteria of the extent 

 and duration of a sporophvtic generation in normal life 

 histories. 



Yet it has become clear from recent research on apog- 

 amy and apospory that the mere number of chromo- 

 somes, whether haploid or diploid, does not determine the 

 morphology of the generation, gametophyte or sporo- 

 phyte, with which they are associated. The reasonable- 

 ness of this principle is apparent when regarded from 

 another point of view. The inheritance which is respon- 

 sible for the development in a type of a sporophyte gen- 

 eration must be carried by the sexual phase, and the 

 potentialities of a sexual generation must be present in 

 the sporophyte, although in normal life histories the in- 

 heritance is latent at certain stages and only becomes 

 operative in both generations after definite periods of 

 development have been passed. The two germ cells, eggs 

 and spores, do not give rise to different generations be- 

 cause they expressly contain a single or a double set of 

 the chromosomes characteristic of the species; the causes 

 of their respective developments are too complicated to 

 be expressed in such simple terms. 



