116 
S. IKENO : 
and PüNNETT have found in F 1 ex HL x bl (purple flower and long pollen by 
red and round) the linkage of the series 7 : 1: 1: 7 between Z> and L, whilst 
in farther generations of the same cross that of the series 15 : 1: 1: 15 has 
been observed ; l also in the same plant and in the same kind of the cross 
Punnett has observed sometimes the 7 : 1: 1: 7 linkage, and sometimes the 
10: 1: 1: 10 one. 2 Again, in the progeny of one of Iris Maize hybrids 
(endosperm horny-waxy, coloured-white) Kempton has generally detected the 
linkage belonging to the series 3 : 1: 1:3, whilst in the progeny derived 
from the same parents he could find that of the series 3:2:2: 3, though 
exceptionally. 3 Recently experiments to modify artificially the amount of 
linkage in Drosophila by the influence of varying temperatures have been 
carried on with success by Plough . 4 The variation of the linkage ratio in 
the cross under discussion is thus no unprecedented fact ; whether it is due to a 
certain change in the internal mechanism, or to the influence of the environment, 
or to certain other reasons is however yet unsettled, and will be the interesting 
subject of future studies. Furthermore, though in our present case we have 
seen the complete linkage of II and D in F 2 and its change into a partial 
in F 3 , it is very doubtful whether such would be always the case. It seems 
to me very probable that there might be several modifications. Thus, for 
instance, the absolute linkage of I\ and JE> seen in F, might remain as such 
in F, ; on the contrary, their partial linkage or even their free combination 
might occur already in F 2 , etc., etc. Still further, some other important 
questions will await the answer. Thus the fact should be determined whether 
the ratio of linkage will remain constant in all cases. Also it will be 
necessary to investigate the fact whether or not this ratio will be equal on 
the male as well as the female side of one and the same plant. As 'one of 
the extreme cases of the inequality of the linkage ratio on the two sides we 
might have, for instance, that where the linkage is complete on one side and 
partial on the other ; nor would it be not impossible that on the one side we 
experimentelle Vererbungslehre, 3. u. 4. Aufl., 1919, p. 172 ff. 
1 Report to the Evolution Committee R. S., Report 4, 1909, p. 11 ff. 
2 Journ. of Genetics, Vol. 3, 1913, pp. 78-79 ; also ibid., Vol. 6, 1917, p. 187. 
3 U. S. Department of Agric., Dull. 754, 1919, p. 78 ff. 
Journ. of experimental Zool, Vol. 24, 1917, pp. 147-209. 
4 
