568 THE AMERICAN NATURALIST. [Vol. XXXIX. 



reduced or modified that the female gametophyte retains the 

 sporophyte number of chromosomes as in the embryo-sac of 

 Alchemilla and Thalictrum the apogamous development of em- 

 bryos is to be expected. 



The discovery of apospory in such variable and perhaps 

 mutating genera as Alchemilla, Taraxacum, and Hieracium sug- 

 gests quite a new line of research with possibilities of a clearer 

 understanding of the origin of mutations. It is very interesting 

 that these widespread and successful genera should give evidence 

 of such strong apogamous habits for it seems to indicate an evo- 

 lutionary tendency in the higher plants of great significance. 

 These forms with Thalictrum are representatives of three large, 

 divergent and very successful orders (Ranales, Rosales, and 

 Compositales) and it suggests the probability that apogamy will 

 be found to be widespread in the spermatophytes. Its bearing 

 on the establishment of extreme variations and mutations may 

 be of the utmost significance for it is clear that the suppression 

 of sexuality would remove sports and mutants at once from the 

 swamping effects of cross-fertilization. The sudden appearance 

 of mutants in some groups and their ability to hold true may 

 indeed be found to rest on the establishment of apogamy in the 

 form. This is at least a possibility which must be considered in 

 cytological investigations on mutants and has not yet received 

 attention. 



The subject of apogamy touches another topic of importance, 

 namely, the theory of homologous generations as contrasted with 

 antithetic generations in comparisons of sporophyte with gameto- 

 phyte. We shall not take up this discussion in detail here. It 

 must have been apparent to the reader that the present treat- 

 ment of the critical periods in the life history of plants is based 

 on the conviction of the correctness of the latter view which has 

 had the support of Celakovsky, Strasburger, Bower, Vaisey, and 

 Klebs. The theory of homologous generations as held by 

 Pringsheim and Scott is admirably discussed by Lang ('98) in 

 connection with his studies on apogamy and also in a briefer 

 note {Annals of Bot,, vol. 12, p. 583). Lang seemed inclined to 

 the opinion that the facts of apogamy and apospory in ferns 

 lent support to the theory of homologous generations since the 



