268 BOTANICAL GAZETTE |APRIL 
It is needless to point out that morphological investigators 
have been concerned with only those stages in the development 
of the individual sporophyte or embryo which constitute the more 
important links of the life cycle, only occasionally illustrating or 
noting the occurrence of several embryos on one gametophyte. 
Sometimes an investigator illustrates a plurality of embryos 
without further comment, and LANG in his work on Helmintho- 
stachys reported a number of embryos only because he made use 
of the arrested embryos of one gametophyte in describing some of 
the missing stages of embryonic development. 
STEPS IN EVOLUTION OF EMBRYONIC SELECTION AMONG PTERIDO- 
PHYTES.—If definite steps in the evolution of embryonic selection 
among pteridophytes are recognizable, these may serve as a rough 
measure of their phylogenetic position, at least of the relative 
position within each of the several well recognized groups. It 
would seem that at least the following stages or steps in the evolu- 
tion of embryonic selection may be recognized 
1. Many sporophytes are found on one vigorous gametophyte, 
a large portion of which reach maturity. Selection may finally 
occur under conditions of crowding in early or later stages, but this 
elimination occurs largely in the environment, and must then be 
recognized as natural selection, as, for example, Tmesipieris and 
Lycopodium with large vigorous gametophytes. 
2. A few sporophytes appear above the soil or break through the 
tissues of the gametophyte, but a selection occurs among a much 
larger number during their embryonic stages; arrested embryos re- 
main turgid for a considerable period, as for example Lycopodium. 
3. One or only very few sporophytes break through tissues of 
gametophytes, but a selection occurs among a large number in 
their embryonic stages; arrested embryos are soon aborted and 
not easily recognized, as, for example, Equisetum, Helminthostachys , 
and Botrychium. 
4. Normally only one sporeling sporophyte is produced, but 
several archegonia are fertilized, and selection between zygotes 
occurs in early embryonic stages; arrested embryos are usually 
soon aborted and not easily recognized, as, for example, Selaginella, 
Osmunda, Aspidium, etc. 
