Robinson 1941 ). German breeders began selecting plants with“low hashīsh con-
tent”(Hitzemann 1941 ; Sengbusch 1956 ; Bredemann et al. 1956 ). Fournier ( 1981 )
bred low-THC plants,“this is probably thefirst time in the world that such action is
taken.”His statement’s hubris is gauling [sic] because the French depended upon
‘Fibrimon’developed by the aforementioned Germans.
Cannabinoid quantity is affected by many genes, and modulated by the envi-
ronment. Genes determine a plant’s chemotype and the expression of
cannabinoid-producing machinery (i.e., density of CSG trichomes, size of resin
heads). Gender is another genetic factor; femaleflowers produce more cannabinoids
than maleflowers. Environmental factors include photoperiod, light quantity and
quality, soil nutrients, and temperature. Valid quantitative comparisons between
plants must minimalize environmental variables. In a common garden experiment
(CGE), plants of different provenances are grown in a single location, under
identical environmental conditions, and uniformly processed.
Fig. 6.2 Cannabinoid biosynthetic pathway, leading to the two major phytocannabinoids, THC
and CBD (courtesy J. McPartland)
140 G. Grassi and J.M. McPartland