284 BOTANICAL GAZETTE [APRIL 
assumes various forms, being represented chiefly by embryonic 
selection, gametophytic selection, and gametic selection. 
2. Developmental selection differs materially from natural 
selection, germinal selection, the intraselection of Roux, as well 
as the other selection theories. 
3. Records of conspicuous cases of polyembryony in ferns are 
brought together. Original studies are added, constituting definite 
evidence that a selective plurality of embryos may normally exist 
even in the leptosporangiate ferns. Nearly all living ferns seem 
to have embryonic selection, or show evidence of having passed 
through a stage in which embryonic selection was the normal 
condition, The embryonic selection represented by the poly- 
embryony of gymnosperms was derived from an embryonic selection 
habit in their fern ancestors. 
4. Developmental selection in gymnosperms and angiosperms 
is not only represented by a selection among embryos, but also by 
a selection between female gametophytes and the male gameto- 
phytes represented by the pollen tubes. 
5. A form of selection intermediate between natural selection 
and developmental selection may be recognized in the competition 
between buds and branches of a sporophyte or a branching thallus. 
6. Developmental selection is a process which brings into play 
a definite internal competition between embryonic diploid individ- 
uals, as well as between the haploid sperms of fern plants, and the 
haploid male and female gametophytes of gymnosperms and 
angiosperms. On the other hand, natural selection usually acts 
on the diploid generation in these plant groups, or on the haploid 
fern gametophytes, where selection may take place in the external 
environment. 
7. The discussion seeks to show why the process of develop- 
mental selection is not open to the more serious objections which 
have been urged against natural selection, and on what basis it 
equals or excels the latter as an effective selective process. 
8. The discussion also shows how developmental selection may 
account for some of the phenomena of orthogenesis on a mechanical 
basis. 
Q. Developmental selection is not responsible for the origin of 
the chromosomal or other intracellular phenomena involved in 
