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AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
Furthermore, the influences that affect the sex of a single flower often 
extend to groups of flowers. Thus there is a period of maleness, which is 
followed by a period of femaleness or of bisexualism, and this in turn is 
followed by maleness. Flowers in the same condition as to sex are grouped 
along the raceme. There is a series of cyclic changes all occurring during 
the period of continuous bloom. 
These qualitative changes in sex in flowers of Cleome spinosa do not 
involve the transformation of organs of one sex into organs of the other sex 
after differentiation has begun, as is the case in many of the intersexes 
reported in animals (Goldschmidt and Poppelbaum, 1914; Goldschmidt, 
1916; Banta, 1916; Lillie, 1917; Sexton and Huxley, 1921). Here the 
change is accomplished, as it is in dioecious plants, by the abortion of one 
or the other kind of sex organs. The relative position of each in the flower 
as a whole is maintained, but the differentiation giving male and female 
flowers (along with bisexual flowers) is as complete as is seen in many species 
of dioecious plants. The differential determination of sex in repeated 
cyclic alternative changes as they occur in Cleome spinosa shows to what 
degree the internal correlative differentiations in development may be 
extended to the organs of sex after the plant as a whole has passed from the 
exclusively vegetative to the reproductive stage. At the time of the transi¬ 
tion to the reproductive stage, the change is not necessarily complete and 
discontinuous, nor are the flowers produced in succession necessarily of the 
same grades of sex. Even when the flowers appear to be morphologically 
the same there may be a decided cyclic change in their physiological char¬ 
acter, as is the case with Brassica chinensis and B. pekinensis (Stout, 1922). 
The contrast between these species of Brassica and Cleome spinosa illustrates 
well the different types of sterility that may develop in plants and the 
different expressions of cyclic regulation of them. In these Brassicas there 
is frequently rather decided abortion of flowers at the time of transition 
from vegetative to reproductive organs; in Cleome no indication of such 
abortion is present, the first flowers to appear being often fully developed 
as hermaphrodites. In the Brassicas there is a somewhat extended period 
of flower formation with flowers all morphologically bisexual—but in which 
the physiological relations in fertilization may vary in a very definite and 
single cycle; in Cleome spinosa there is no variation in the physiological 
nature of stamens and pistils that are at all functional in so far as these 
may be tested by the relations of fertilization, but there is the cyclic alter¬ 
nation in the morphological development of the organs of sex. This 
comparison illustrates two rather widely different expressions of sex in its 
relation to fertility and sterility. 
The conditions in Cleome spinosa favor the view that, as held by Yam- 
polsky (1920), there is a general tendency away from hermaphroditism 
toward dioecism among the higher plants. In the persistence of perfect 
flowers in greater or less numbers along with those which are more or less 
