_ SCHAFFNER: SEXUAL STATE IN SAGITTARIA LATIFOLIA IIT 
sufficient intensity at the very beginning of the development of 
the gametes, the greatest dimorphism results. The hetero- 
gametes of the higher organisms, whether plant or animal, 
are not different in general aspects from those near the base of 
the evolutionary series. 
The evolution of the secondary sexual states and characters 
is along exactly similar lines. In the simple sexual plants and 
in gametophytes with an alternation of generations, there is a 
progression from the condition where dimorphism arises only 
at the end of the ontogeny in cells and tissues immediately con- 
tiguous to the gamete-producing cells, and the progression leads 
backward from this condition through sex determination at 
earlier and earlier stages of the ontogeny until the entire in- 
dividual is involved, the determination of sex taking place, or 
being already determined, in the spore from which the gameto- 
phyte arises. 
Finally, there is an exactly similar progression in the evolution 
of sexual states in the sporophyte. In the lowest heterosporcus 
sporophytes the secondary sexual states arise side by side at the 
end of the ontogeny, namely, when the sporangia are produced, 
just as they do in the primitive hermaphrodites. Then the 
different types fall into an orderly progression of earlier and 
earlier sex determination; first the male and female states arising 
in the same sorus, second in separate sori of the same leaf, and 
third in entirely different sporophylls, giving rise to bisporangiate 
flowers. This condition remains in most groups even to the very 
highest. From the condition of bisporangiate flowers there are 
various types and degrees of moneciousness, with the sex deter- 
mined at the base of or keyond the floral axis, up to the complete 
diecious condition. The determination of sex is again thrown 
back into earlier and earlier stages of the ontogeny until it coin- 
cides with the development of the female gamete or the time of 
its fertilization. 
In view of these evident conditions and the nature of sexual 
expression in monecious plants together with the fact that the 
sex of diecious sporophytes can be reversed in both directions, 
the writer* in an earlier paper said that the characters of an 
* SCHAFFNER, JOHN H. Progression of sexual evolution in the plant 
kingdom. Ohio Jour. Sci. 22: 101-113. 1922 
