Nov. 15,1925 
The Genetics of Sex in Hemp 
941 
results of breeding experiments reported by Correns (2, 3 ), and the 
case of sex-linked inheritance of the XY type in this species reported 
by Shull (13), are in accord with the results of these cytological 
investigations. The presence of a visible chromosome difference in 
Humulus lupulus and in H . japonicus has also been shown by Winge 
(15). In both species the staminate type is heterogametic. So far 
as the writer is aware, there are no published results of breeding 
experiments to substantiate this finding. 
Recently Kihara and Ono (6) have reported a peculiar chromo¬ 
some condition in Rumex acetosa. The carpellate form contains 2 
large M chromosomes and 12 autosomes. The staminate form con¬ 
tains 12 autosomes and 1 large “ tripartite,'' which consists of a 
large M chromosome and two smaller elements. It is assumed that 
the large M is the X chromosome and the smaller elements the Y 
chromosome. Such a condition is in line with the results of Corren’s 
(4) breeding experiments, from which he inferred that two kinds of 
pollen were being produced. 
The evidence obtained from these sources shows that sex chromo¬ 
somes exist in at least some of the dioecious species of plants. A 
fact of still greater importance is that both the genetic and cytological 
evidence points to the heterozygousness of the male form. It may 
seem, therefore, that a simple and general hypothesis should explain 
the mechanism of sex determination in such dioecious species. So 
little is known of the genetics of each species, however, that it seems 
to the writer that the accumulation of more genetic evidence should 
be awaited before a general hypothesis is formulated. For this reason 
the writer wishes to restrict to hemp his suggestions concerning sex 
in plants. 
It has been repeatedly maintained during recent years that sex 
determination and segregation in dioecious species of plants has noth¬ 
ing to do with the segregation of the chromosomes, because sex is not 
determined until long after the reduction division and fertilization 
have taken place. Let us examine the evidence for such a contention 
in the case of hemp. It is not possible to distinguish between the 
carpellate and the staminate plants before the vegetative differences 
are developed or the flower buds appear. That is, during the early 
stages of growth all the plants appear to be the same. Is it to be 
assumed that the sex of such plants is not determined until just prior 
to the appearance of the flower buds ? Is it to be assumed that in a 
plat of 10-day-old hemp the plants are neither staminate nor carpel¬ 
late? The fact that it is impossible to distinguish the sexes one from 
the other at this stage of their life is not critical evidence that the 
sexual type has not been determined. If it could be shown, for in¬ 
stance, that in a plat of 1,000 plants all could be caused to develop 
into the carpellate type, there would be strong reason for believing 
that the sex of the individual is determined some time after the seed 
has germinated. But man has been unable to do this sort of thing, 
no matter what methods were used. Of course it has been shown 
repeatedly that as high as 90 per cent of plants in certain plats devel¬ 
oped flowers of the opposite sex. Whether these flowers were the 
same genetically as those produced by the normal staminate or car¬ 
pellate type is the really critical evidence which is lacking for these 
numerous cases. And until more of such evidence is available the 
