June 14, 1924 
Influence of Environment on Sex in Hemp 
1071 
sex ratio was 128:100 in a population of 128. At maturity the mean height of 
the entire lot was only 0.21 meter and the majority of the plants had to be 
supported. It is evident that this length of day approaches the lower limit in 
which hemp can be grown to the flowering stage. 
Seven-hour exposure. —An increase of 2 hours daily over the 5-hour exposure 
not only caused the plants to develop buds 7 days sooner but also caused a 
significant increase in the development of vegetative and reproductive parts. 
The mean height attained was 0.50 meter and the stems were sufficiently strong 
to stand without support. The sex ratio was 119:100. 
Ten-hour Exposure. —The chief difference shown by this lot of plants was 
one of greater development. The mean height at maturity was 0.75 meter, 
leaves were large and deep green in color, and flowers were very abundant. 
Buds appeared 33 days from date of planting which is practically the same 
length of time required by plants in the 7-hour exposure to develop buds. The 
sex ratio was 111:100. 
Full day in dark-house. —The lot which was grown in the dark-house but 
exposed to the normal length of day for this latitude made so much growth that 
the size of the pot probably was a limiting factor in their development. The 
mean height at maturity was 2.05 meters. The main stem did not develop 
proportionally in thickness but remained slender and many of the plants were 
unable to support themselves at the time of flowering. The leaves were large 
and numerous but side branches were not produced to any extent. The time of 
flowering was greatly delayed in this lot by the long daily exposure to light, 
buds first appearing 84 days from the date of planting. The sex ratio was 
115:100 in a population of 73. 
Full day outside in pots. —A number of plants were grown in 5-inch pots 
in the open as a control on the lot which was grown in the dark-house. Flower 
buds appeared in 80 days from date of planting. Due to inability to properly 
control the moisture content of the soil, growth was somewhat irregular and the 
results obtained with this lot are not comparable with the results obtained with 
the other lots. The mean height at maturity was 1.04 meters and the sex ratio 
140:100 in a population of 120. 
Planted in the garden plat. —Hemp which was grown in the garden plat 
attained a much larger size than did any of the potted plants. The mean height 
at maturity was 3.38 meters, although individual specimens reached a height 
of over 4.5 meters and a main stem diameter of over 1 inch. Side branches were 
produced in large numbers and flower production was very profuse. It is a 
significant fact that although this lot made a much greater vegetative develop¬ 
ment, they produced flower buds at the same time as did the lot which was grown 
in full-day exposure in the dark-house. This result indicates that the differences 
in development are due to factors other than light and that the time of flowering 
is not determined by the extent of vegetative development. The sex ratio of 
the plants in the garden plat was 97:100, the nearest to unity of any of the lots, 
but of course this is probably only a matter of coincidence. 
EFFECT OF LENGTH OF EXPOSURE TO LIGHT ON GROWTH 
The results show that both the rate and extent of growth, as well as the time 
of flowering, are greatly affected by the length of daily exposure to light. The 
effect on vegetative and sexual development can best be discussed separately. 
