Pubdate: 1947
Source: The Yearbook of Agriculture; 1943-1947, United States Department

of Agriculture
Author: H.A. Borthwick, USDA Senior Botanist in the Bureau of Plant Industry,

Soils, and Agricultural Engineering
Pages: 282-283

DAY LENGTH AND FLOWERING - HEMP

Most rapid progress in breeding plants can be made with those that can be

self-pollinated. Hemp, obviously, can be self-pollinated only when it produces

these occasional additional flowers of the opposite sex. The advantage of

being able to increase their tendency to form these flowers is apparent.

Dr. Hugh C. McPhee of the Department made use of this behavior of hemp

several years ago.''' He used the pollen of the male flowers that were

produced in small numbers on certain of the female plants to self-pollinate

those plants. When he grew the resulting seeds he made the important

discovery that all of the plants were female. We have recently produced

several thousand seeds in this way and have not obtained a single male plant,

thus thoroughly confirming Dr. McPhee's observations'''.

Under greenhouse conditions, with proper control of temperature and day

length, a very high percentage of female plants produced enough male

flowers so that self-pollination could be effected, and in certain experimental

lots of female plants produced out-of-doors in late summer when days were

short and nights were cool, enough male flowers were formed so that natural

pollination occurred and a quantity of pure "female" seed was produced.

These results suggest that a locality can be found in which the conditions are

favorable to the formation of these intersex male flowers on female plants in

sufficient quantity that a good crop of seed could be obtained. If this could be

done, a means would be at hand to produce commercial quantities of

"female" seed, thereby enabling growers to produce a pure stand of female

plants. Such pure stands would result in a more uniform fiber crop and

eliminate certain harvest problems. The basis for developing such a

procedure lies in finding in nature a combination of environmental factors

similar to that which, under experimental conditions, has resulted in formation

of abundant male flowers.


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