1080 
Journal of Agricultural Research 
Vol. XXVIII, No. 11 
of high growth rate is correspondingly shorter and the plants attain a height of 
only 1 to 2 feet. The growth rate of hemp grown in a short daily exposure to 
light may, however, at some time in its life exceed the growth rate of hemp 
grown in longer daily exposures. 
3. The time of flowering of hemp is largely controlled by the relative length of 
day and night. A daily exposure to light of ? hours seems to produce the greatest 
acceleration of the flowering process. A longer or a shorter daily exposure pro¬ 
duces a retarding effect on flower development. 
4. Three hours of light daily is the least in which hemp will grow for any 
length of time. If a shorter period of daily illumination is used the plants die 
before reaching the flowering stage. 
5. It is not possible to retard the length of daily period of illumination suffi¬ 
ciently to prevent flowering without causing the death of the plants. 
6. “Sex reversal” does not necessarily result when hemp is grown in the 
greenhouse during the winter months. More intersex types are found under such 
conditions, but many of the plants remain sexually pure. We may conclude 
that environment in some way affects the development of sex in this species, but 
the evidence shows that it does not control it. 
7. Removal of flowers does not necessarily result in sexual modifications in 
hemp, although a few plants so treated and grown in a short daily exposure to 
light reversed their sex to the extent that some apparently pure staminate indi¬ 
viduals matured seed. The occurrence of this phenomenon was not sufficiently 
general, however, to allow definite conclusion^ to be drawn. The removal of 
flowers from hemp which is grown in the field is without effect in causing sexual 
changes. 
8. Although the development and expression of sex in hemp are affected by 
environmental factors, the changes produced are in many cases relatively minor 
ones, and a sweeping conclusion that genetic factors are in no way concerned 
with sex in this species is not warranted at the present time. 
LITERATURE CITED 
(1) Garner, W. W., and Allard, H. A. 
1920. EFFECT OF THE RELATIVE LENGTH OF DAY AND NIGHT AND OTHER 
FACTORS OF THE ENVIRONMENT ON GROWTH AND REPRODUCTION 
in plants. Jour. Agr. Research 18: 553-606, illus. 
( 2 ) - 
1921. FLOWERING AND FRUITING OF PLANTS AS CONTROLLED BY THE 
length of day. U. S, Dept. Agr. Yearbook 1920: 377-400, 
illus. 
(3) - 
1923. FURTHER STUDIES IN PHOTOPERIODISM, THE RESPONSE OF THE 
PLANT TO RELATIVE LENGTH OF DAY AND NIGHT. Jour. Agr. 
Research 23: 871-920, illus. 
(4) Pritchard, F. J. 
1916. change of sex in hemp. Jour. Heredity 7: 325-329, illus. 
(5) SCHAFFNER, J. H. 
1919. complete reversal of sex in hemp. Science 50: 311-312. 
( 6 ) - 
1921. influence of environment on sexual expression in hemp. 
Bot. Gaz, 71: 197-219, illus. 
(7) - 
1923. THE influence of relative length of daylight on the re¬ 
versal of sex in hemp. Ecology 4: 323-334. 
(8) Tournois, J. 
1911. ANOMALIES FLORALES DU HOUBLON JAPONAIS ET DU CHANVRE 
d:etermin£es par des semis hAtifs. Compt. Rend. Acad. Sci. 
[Paris] 153: 1017-1020. 
