CHANGE OF SEX IN HEMP 
Mutilation Makes Female Plants of Cannabis Sativa Produce Male Flowers— 
Change in Nutrition Probably Responsible for the Result 
FREDERICK J. PRITCHARD 
Bureau of Plant Industry, U. S. Department of Agriculture, Washington, D. C. 
sex ratios in dioecious species of 
plants and animals is one of the 
most debatable topics of genetics. 
The experimental results thus far re- 
corded are not only varied but occa- 
sionally contradictory. When viewed 
as a whole, however, they seem to indi- 
cate that maleness and femaleness are not 
always fixed characters, but frequently 
appear more like responses of the devel- 
oping organism to external stimult. 
Of all the external factors that have 
been supposed to determine sex, food 
ranks first. Indeed, many biologists 
now believe that the determination of 
sex is in the last analysis a problem of 
nutrition. It is also remarkable that 
in nearly every instance in which food 
affects the sex ratio, favorable nutritive 
conditions tend to produce females and 
unfavorable conditions males. 
Nevertheless the food theory of sex de- 
termination fails to account for the sex 
ratio of 1:1 commonly found among 
unisexual individuals. 
A Mendelian theory of sex deter- 
mination now popular not only explains 
normal sex ratios in dioecious species 
but receives considerable support from 
studies of sex-linked inheritance. The 
fundamental basis of this theory as 
expressed by a distinguished geneticist 
is that “‘sex has its beginning in gametic 
differentiation and is finally determined 
beyond recall in the fertilized egg by 
the nature of the uniting gametes.” 
The hypothesis also carries the assump- 
tion that one of the sexes is heterozygous 
for a sex factor and the other homozy- 
gous. 
Though subject to criticism, this 
theory is admirably adapted to the 
factorial method of analysis and appears 
to explain many facts of sex inheritance. 
[= possibility of altering normal 
The difference of opinion regarding 
the effect of external stimuli upon sex 
ratios has led the writer to investigate 
the following questions: (1) Can sex 
ratios of dioecious plants be altered by 
modifying conditions external to their 
germ cells? (2) Is the alteration thus 
obtained limited to individuals of one 
sex? (3) How do the results harmonize 
with the Mendelian conception of sex 
determination? 
MATERIAL 
As hemp is composed almost wholly 
of distinctly unisexual individuals it 
was chosen as a favorable species for 
the investigation of sex ratios. In 
addition to its separation of the sexes, 
it develops in its females a heavy and 
dense growth of foliage by which they 
may readily be distinguished from the 
males. In fact, at the time of flowering 
the plants may be recognized at a 
distance as male and female. 
The proportion of males to females 
which normally appeared under the 
field conditions where the experiments 
were made was approximately 1:1. 
Monoecious individuals aiso appeared 
in relatively small numbers, as will be 
subsequently shown, but they were 
distinctly female in type and prepon- 
- deratingly female in flower development. 
METHODS 
Disturbances of the plant’s physio- 
logical equilibrium were induced by the 
removal of flowers and vegetative parts 
and by the injection of chemical sub- 
stances into the stem. 
In addition to the removal of parts 
some plants were given further treat- 
ment by enclosing their tops in Manila 
bags to diminish the intensity of the 
light falling upon the newly developing 
flower buds. 
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