SEX INTERGRADATION IN THE FLOWERS OF MERCURIALIS ANNUA 99 
pollen and the ovules suggest that total sterility does not occur. Gold- 
schmidt (1916), in his crosses between European and Japanese races of the 
gypsy moth, Lymantria dispar, secured individuals that showed gradations 
in maleness and femaleness. Such a condition was usually accompanied 
by sterility. Banta (191 6, 191 8) finds that in his Crustaceans the more 
pronounced the sex intergradation the more sterile the form became. 
While a flower of a plant may not be compared to an individual like a moth 
or a Crustacean, it is interesting to note that in plants sex intergradation 
is not, as a rule, accompanied by sterility. On the contrary, the plants 
whose flowers were studied showed no diminution in seed production or in 
general vigor. 
The condition of intergradation within a series of flowers on a single 
plant brings up interesting considerations bearing upon the question of 
when and how the sex of each flower is determined. The Anlagen or deter- 
miners, if there be such, must be different for the different flowers according 
to the arrangement of their parts. It must be borne in mind that in this 
so-called monoecious form of Mercurialis the sex of the plant changes in 
the course of the plant's development. The initial flowers are female. 
Several weeks after germination the young plant produces female flowers, 
and only female flowers are produced for several months. Then a few 
male flowers or hermaphroditic flowers appear. These increase in number 
as the season advances. As far as the whole plant is concerned, there is 
a periodic alteration of sex. A factorial hypothesis for sex cannot explain 
these results. It would seem logical to assume that the sex of the flower is 
determined at the time of its formation and not when the plant of which 
it is a part is in the fertilized egg stage. Moreover what seems to hold true 
for such flowers as represented in figure i to 7 apparently does not hold for 
the aberrant conditions I have noted. In the various transitional forms 
there seems to be no definite factor which determines the sex of the flower; 
pistil passes into stamen and stamen into pistil at any time in its develop- 
ment. The argument for strict sex segregation is obviously nullified because 
of the behavior of these forms. The line of demarcation between what is 
male and what is female is wavering and vague. The evidence brought 
out here tends to emphasize an epigenetic condition for sex rather than the 
presence of definitely localized qualitative or quantitative factors. 
LITERATURE CITED 
Banta, A. M. 1916. Sex intergrades in a species of Crustacea. Proc. Nat. Acad. Sci. 
2:578-583. 
. 191 8. Sex and sex intergrades in Cladocera. Proc. Nat. Acad. Sci. 4: 373-379. 
Goldschmidt, R. 191 6. A preliminary report on further experiments in inheritance and 
determination of sex. Proc. Nat. Acad. Sci. 2: 53-58. 
Haring, J. 1894. Abnorme Kaetzchenbildungen bei Salix caprea L. und bei Salix cinerea 
L. Oesterr. Bot. Zeit. 44: 386-387, 415-418. 
Yampolsky, C. 1919. Inheritance of sex in Mercurialis annua. Amer. Journ. Bot. 6: 
410-442. 
