568 THE AMERICAN NATURALIST. | (Vot. 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 (798) in 
connection with his studies on apogamy and also in a briefer 
Sone. rum 
lent support to the : ng on UE : peu 
eory of homologous generations since the 
