dietary use of hempseed oil, hempseed production has become a significant sector.
Indeed, the economic prospects for continued development as an oilseed crop are
considerably better than for continued development as afiber crop.
1.6.3.2 Architecture and Anatomy
There is evidence of land races ofC. sativaspecialized forfiber or THC production
being grown for centuries, perhaps for millennia, but the same is not true for oilseed
hemp. Rather, it appears that seeds were simply harvested from plants grown for
fiber or drugs. Since plants grown for THC produce manyflowers (the bracts of
which bear the large secretory trichomes mainly responsible for THC production),
they are much more suitable for yield of many seeds. However, when most land
races offiber hemp are grown well-spaced, they too become relatively branched,
producing many moreflowers than when crowded together forfiber yield. Because
considerable branching is a characteristic that maximizes seed production, it is
probable that in historical times farmers who favored seed production probably
selected genotypes with this propensity (Fig.1.5a).
Until very recent times, the widespread cultivation of hempprimarilyas an
oilseed was largely unknown, except in pre-World War II Russia. The kind of
Russian land races once grown as oilseeds are doubtfully still extant, but it appears
that some were distinctly short with a compact highly branched infructescence.
Today, there are only a few cultivated varieties currently available that have been
bred specifically for the production of grain, but the most productive are recently
created short varieties with a compact highly branched infructescence (Fig.1.5b, c).
It appears that modern hempseed breeders have intuitively or intentionally recon-
structed the kind of plant that used to be grown in Russia for oilseed. Low stature is
desirable in oilseed selections to avoid channelling the plants’energy into stem
tissue, in contrast tofiber cultivars for which a very tall main stalk is desired.
Compact clustering of seeds also decreases stem tissue, promotes retention of seeds
and facilitates collection.
The efficiency of grain production by crops is often measured by“harvest
index,”the ratio of harvested grain to above-ground dry matter, and crop breeders
are strongly motivated to increase the harvest index by maximizing grain yield
while minimizing other plant tissues. Modern selection is also occurring with regard
to mechanized harvesting, particularly the ability to grow in high density as
single-headed stalks with very short branches bearing considerable seed, an
architecture that not only maximizes harvest index but also facilitates machine
harvesting. As well, a highly congested fruit axis (adjacent seeds very close
together along with bracts and young leaves; Fig.1.5c) makes it very difficult for
seeds to fall away from the plant, and facilitates harvest of the seeds. Plants with
limited (or at least compact) branching are naturally superior to irregularly
1 Classification ofCannabis sativaL. in Relation... 19