OCCURRENCE AND INHERITANCE OF SEX INTERGRADATION IN PLANTS 29 
dioecious, gradations in sex like those described for other forms. They 
find a small proportion of monoecious plants which represent all gradations 
between the normal pistillate and staminate types. They also describe 
bushes and shoots whose sex may vary from year to year. Fourteen cases 
found to be entirely pistillate in 1913 and 19 14 produced staminate catkins 
in 1915. One plant produced almost entirely staminate catkins. Certain 
trees and branches which produced abundant fruit in 191 3 developed mixed 
shoots in 1914 and in 1915 became almost staminate. 
The classic case of alteration of sex in plants is that of Lychnis dioica 
when attacked by the anther smut fungus, Ustilago violacea. Strasburger 
(1900) points out that both male and female plants are attacked by the 
smut. In the anthers of the male the parasite causes a characteristic 
purplish color, the interior of the anther being filled with smut spores. 
In the female the fungus causes a more profound change. The plant is 
stimulated to produce anthers with the characteristic sporogenous tissue 
which tissue is later destroyed by the fungus so that the anther is ultimately 
filled with fungus spores. 
Although the list which I have brought together is by no means com- 
plete, it is, however, sufficiently representative of the changes in sex that 
have been reported in the literature. Sex intergrades, it will be noted, may 
occur in various degrees, from the transition of one sex organ into that of 
the opposite sex to a complete change of sex of the entire plant. 
Secondary Sex Characters 
It is to be noted that inter^exualism in animals is measured by the degree 
of modification of one or the other of the secondary sex characters, by the 
appearance of secondary sex characters of one sex in individuals of the oppo- 
site sex, as well as by the degeneration of ovary or testis or the transition of 
an ovary into a testis or of a testis into an ovary. In animals sex dimorph- 
ism is the characteristic thing, and one is familiar with such differences in 
sex as size, voice, stature, plumage, and the like. 
Sex dimorphism in flowering plants, where the sexes are separate, is 
not very striking; secondary sex characters have been contrasted but little 
in such forms. Darwin (1889, page 11) cites the case of the Resteaceae of 
Australia and the Cape of Good Hope, forms which show extreme sex 
dimorphism. It is reported that often it is impossible to match the male 
with the female of the same species. Shull (1914) reports for Lychnis 
dioica L. a sex-limited character in the form of narrowness of leaf in the 
male of Lychnis dioica angustifolia. Cook (19 14) reports on a case of sex 
inequality in hemp, where the male plants are smaller and shorter than the 
females. These male plants die much sooner than the females. 
The female inflorescences of Mercurialis are borne in clusters in the 
axils of the leaves, while the male inflorescences are borne in interrupted 
spikes which surpass the leaves. This characteristic appearance of the 
