INHERITANCE OF SEX IN MERCURIALIS ANNUA 4II 
my preliminary report (19 16) I have indicated that such plants may be 
regarded as sex intergrades in the light of Goldschmidt's (1916a, h) results 
with moths. An examination of tables I, 3, and 6 of this paper will show 
the variations in the number of male flowers produced upon the female 
plants and in the number of female flowers upon the male plants. The 
number of male flowers found on the female plants varied from i to 32, and 
the number of seeds set on these plants varied from I to 230. On a so- 
called male plant approximately 25,000 male flowers are produced at one 
time (see page 420). The number of female flowers upon the male plants 
varied from i to 47 and the number of seeds set varied from i to 93, while 
on a so-called female plant thousands of seeds may be produced. Sex 
gradations may be recognized, starting with the pure female at the one ex- 
treme and the plant that produced 230 seeds at the other; the remaining 
plants are graded between these two. Sex gradations in the male may be 
noted starting with the pure male as the one extreme and the plant that 
produced 93 seeds as the other; the remaining plants will grade themselves 
between these. As described below, I have also had monoecious forms 
which produce male and female flowers in approximately equal numbers. 
The species is described as dioecious, occasionally monoecious, by Engler 
and Prantl (1897). 
Plates XXXVIII and XXXIX bring out the characteristic differences 
in the appearance of the male and female plants of Mercurialis annua. 
The pistillate flowers of the female are clustered in the axils of the leaves, 
while the staminate flowers of the male are in interrupted spikes which 
surpass the leaves. 
It has been shown by Bitter (1909) that the seed produced upon isolated 
female plants is due to fertilization by pollen from occasional male flowers 
produced on the female, and that it is not a parthenogenetic phenomenon. 
The appearance of male flowers on the female plants is sporadic. They are 
inconspicuous and difficult to detect. In my work the entire plant was 
examined at intervals of three days and oftener for the appearance of male 
flowers. 
Two months after the observations were begun (in the middle of April), 
two male flowers were found upon the apices of two side branches. Each 
male flower bore eight stamens. There was no evidence of a vestigial or 
aborted ovary. A microscopical examination of the pollen grains of several 
of the anthers showed them to be plump and to all appearance healthy. 
An examination twenty-four hours later showed the anthers to be shriveled 
and about to drop off. In a few days some of the ovaries in the vicinity of 
the male flowers showed noticeable swelling. 
Continued examination of the plant showed variations in the disposi- 
tion of the male elements. I found five distinct types of arrangement of 
the pistils and stamens. Normally there is a two-celled ovary which 
splits at maturity, each cell containing one seed (fig. A). Occasionally 
