Just to show everyone that hemp research and production was NOT abandoned
after World War II let me submit the following article from "Fibres
(Engineering and Chemistry)" October, 1956:

"Monoecious Hemp Breeding in the United States" Carl V. Feaster
Agronomist, Field Crops Research Branch, Agricultural Research Service,
U.S.D.A.

Isn't it curious that this historic document was published in a British
Journal?

The hemp breeding programme in the United States is being directed
toward improvement of fibre quality through the development of strains with
uniform maturity among plants. Present commercial varieties are dioecious,
with the male plants returning about three weeks before the female plants.
This results in fibre of different maturity and consequently less
uniformity.
The development of monoecious strains, where all plants mature at
approximately the same time, is an effective means of eliminating much of
the variability in fibre quality among plants. Monoecious hemp also may
allow for changes in processing methods to the extent that water retting
would be economically feasible. At present, hemp in the United States is
dew retted.

Trials and results
The original monoecious plants were selected by Borthwick and Scully*,
while conducting photoperiodic studies with Kentucky hemp, a dioecious
variety. This material was released to the Hemp Improvement Project and a
monoecious hemp has been developed by several generations of sibbing
selected monoecious plants. The monoecious character has become relatively
stable. A few female plants appear in some strains; however, no male
plants occur unless foreign pollen is involved.
Yield trials comparing Kentucky hemp with Kentucky monoecious show the
yield of fibre to be about the same for the two varieties; however, the
percentage of fibre has averaged slightly higher for the dioecious variety
and the stalk yield slightly higher for the monoecious variety.
Evaluation of individual plants from Kentucky monoecious showed
considerable variation in the percentage of fibre, stem weight, stem
weight, stem diameter, and weight/diameter ratio of the stem. Per cent
fibre was negatively correlated with the other measured characters. That
is, plants with low stem weight, small stem diameter, or weight/diameter
ratio of the stem were relatively high in per cent fibre. When the
progenies from these selected selfed plants were grown, heritability was
found to be high for per cent fibre but was negligible for stem weight,
stem diameter, and weight/diameter ratio of the stem. These results
indicate that although stem weight, stem diameter, and weight/diameter
ratio of the stem is correlated with per cent fibre, the stem measurements
do not express the inherited phase of per cent fibre. The measurements do,
however, account for some of the differences in per cent fibre which are
due to environment. When proper adjustment of per cent fibre was made on
the basis of stem weight, stem diameter, or weight/diameter ratio of the
stem, the variability due to genetic differences was more evident and
selection of plants inherently high in fibre was more effective.
The genetic variability and heritability of a character is indicative of
the extent to which improvement is possible through selection. Improvement
of fibre content within this strain appears promising since it is
relatively heterozygous for per cent fibre and heritability of per cent
fibre is high.
Some of the details of the above work appear in an article entitled
'Genetic and Environmental Variability of Percent Fibre and Other
Characters in Monoecious Hemp, Cannabis Sativa L.' The Textile Quarterly,
Volume 6, No. 1

*Borthwick,.A., and Scully, N.J. Photoperiodic Responses of Hemp. The
Botanical Gazette 116; 14-29. September 1954

(I'll post Borthwick and Scully when I get time...stay tuned.)

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