1068 
Journal of Agricultural Research 
Vol. XXVIII, No. 11 
Carpellate plant: More vigorous but shorter than the staminate type; terminal 
inflorescence leafy; broad crown of leaves; flowers with perianth but no vestiges 
of stamens; weight at maturity about twice that of the staminate type; longer 
life. 
Probably hemp is as dioecious as any of the so-called dioecious species but 
it is a well-known fact that certain individual plants sometimes bear both stam¬ 
inate and carpellate flowers at the same time, and that such intersex types 
appear in larger numbers when the daily exposure to light is short, such as 
prevails in northern latitudes during the winter months. The vegetative dif¬ 
ferences, however, are the same for the plants which remain sexually pure and 
for those which develop some flowers of the opposite sex. That is, a change in 
the sex of the flowers produced is not accompanied by a corresponding change 
in the vegetative characters. In other words, the dimorphic vegetative types 
occur in approximately a 1:1 ratio. It seems quite clear that probably the 
vegetative type of the plant was already determined in the embryo from which 
the plant grew but that the sex of each flower was not determined until a some¬ 
what later stage. The natural thing is for each vegetative type to produce 
flowers of the sex characteristic of that type but so far as any differences which 
exist in the structural elements of the two types are concerned there is no reason 
why both sexes of flowers can not be borne by both staminate and carpellate 
plants. The common occurrence of intersex types in the greenhouse shows that 
this is true. The writer has several times grafted staminate tops on carpellate 
stocks and vice versa without any effect upon the sex of the flowers, but does 
not mean to say that pollen which is produced by a carpellate type plant is the 
same genetically as that produced by a staminate plant. But since this paper 
is concerned only with the effect of environmental factors, a discussion of the 
hereditary aspects of the case will be deferred until a later paper. 
PRELIMINARY OBSERVATIONS 
The writers attention was first directed to the effect of relative length of day 
and night upon sex in hemp by the peculiar behavior of several specimens which 
were being grown in the greenhouse during the late winter and early spring 
months. The seed was planted about the first of December and flower buds were 
first distinguishable on January 4. Relatively few flowers were produced 
and many of these were so abnormal that few seeds were matured. Following 
the maturity of this crop of seed the plants remained quiescent for several weeks 
and then resumed growth during the late spring months flowering again at about 
the normal blooming time for hemp which is grown in the open. It was thus 
possible to cause two crops of flowers to be produced in one year. The flowers 
which were produced during the second flowering period were normal and a fair 
crop of seed was matured. The same general effects are produced when hemp 
which has been planted in the open is moved into the greenhouse in the fall. 
The writer moved several such plants into the greenhouse before killing frosts 
occurred to ascertain if they could be held over in a semidormant condition. 
These plants dropped most of their leaves and made no additional growth for 
several weeks. During the month of December new leaves appeared and a small 
number of flowers were produced, most of which were abnormal. The production 
of flowers was still in progress when the plants were discarded late in January. 
This case refers only to carpellate forms, since the staminate plants die in late 
summer and apparently can not be kept alive by moving into the greenhouse. 
The sexual abnormalities which appear during the short winter days are of the 
diverse kinds. The most common type among the plats has been the production 
of intersex flowers on plants of the staminate type. The individual flowers in 
