940 
Journal of Agricultural Research 
Vol. XXXI, No. 10 
other characters does not signify that the genetics of the case is any 
less important. 
The key to the situation is evidently to be found in the mechanism 
which controls the sex ratio under normal cultural conditions. The 
simple assumption that one sex is homozygous and the other hetero¬ 
zygous would explain the occurrence of the 1:1 sex ratio. A 
cross between such types is expected to produce equal numbers of 
each type. The data presented in Tables II and III indicate that 
the carpellate type is the homozygous one. Then, the carpellate form 
might be represented by the symbols XX and the staminate type 
by the symbols XY. The selling of a carpellate type or crossing 
with another carpellate-type plant would be expected to produce 
only carpellate-type individuals. The selfing of a staminate-type 
individual would be expected to give rise to carpellate, staminate, 
and YY individuals in the ratio 1:2 : 1. The nature of the YY 
form, if such exists, is a question on which data are lacking at pres¬ 
ent. Otherwise, the data thus far obtained can be explained on 
such a provisional hypothesis. It is not to be assumed^ however, 
that the condition is as simple as such a hypothesis might lead one 
to believe. The data available concerning the progeny of a selfed 
staminate-type plant consists of only 4 individuals, of which 3 were 
staminate and 1 was carpellate. This is entirely too small a number 
of individuals to be of any significance and can be of use only in 
suggesting that the staminate type is heterozygous for the sex factors. 
This is a point which must be cleared up by further investigation. 
If the staminate type is hererogametic, it may be assumed that 
there exists a chromosome difference between the two kinds of gametes 
produced. Cytological investigations, however, have failed to show 
any such differences. The investigations of Strasburger ( 14 ) and 
of the writer (8) have shown that there is apparently nothing in the 
chromosome complex of hemp which can be identified as a sex 
chromosome. The 20 pairs of chromosomes are so nearly the same 
size and shape that it is not possible to follow them individually 
through the stages of cell division. But of course this evidence 
does not preclude the possibility that one pair of chromosomes is 
carrying the sex genes. There is no reason why the chromosome 
which carries the genes for sex should have a hook on one end or 
be larger than any of the others. This condition does exist in some 
animals and plants, but it does not follow that there is a correlation 
between the presence of sex genes and size or shape of the chromo¬ 
somes which carry them, x 
During recent years a vigorous search for sex chromosomes in 
dioecious species of plants has been in progress. The results, positive 
in many cases, indicate that the male sex is heterogametic. Such a 
condition being in accord with the results obtained in breeding 
experiments with hemp, it seems desirable to mention the outstand¬ 
ing cases. 
The presence of sex chromosomes in Lychnis Jioica has been shown 
by Winge (16). The female plants contain 22+ XX and the males 
22+XY. This condition has been confirmed by Blackburn (I), 
who finds the diploid number to be 24, of which 2 are larger than the 
other 11 pairs. In the staminate plants, one of the pair differed 
from the other in respect to both length and shape. The interesting 
