74 H. NILSSON-EHLE 
the same essential kind as those found in an ever increasing degree 
in many other plants. 
8. Chapter V discusses the possibility of regarding partial he- 
lerogamy as a case of partial sex-linkage and reasons are given 
‚for the identifying of partial heterogamy with partial linkage in wheat, 
caused by increased difficulty for the exchange of genetic factors, that 
is, Obstacles to free recombination of factors. 
9. The absence of heterogamy in some speltoid-series and the 
presence of it in others is probably due to the specific genetic charac- 
ter of the speltoid-mutation. The greater the complex-mutation (see 
my paper 1920), that is, the greater the alteration of the genetic 
constitution, the greater the tendency to heterogamy. A crossing 
speltoid (belonging to a non-heterogamous series) X heterozygote 
(in a heterogamous series) gives new heterozygotes, whose pro- 
geny is not heterogamous. Through the mutation an alteration in the 
cell-structure may be inferred, which renders the mendelian exchange 
of factors more difficult. The heterogamy is thus caused by the 
genetic character of the mutant, in the same manner as in Matthiola 
the heterogamy obviously is due to the genetic character of that spe- 
cific »single» (as opposed to the normal single), that is present in the 
eversporting-strain (Chapter VI). 
10. In Chapter VII a somewhat dubious series in summer-wheat 
is accounted for which at first (1917) was described as non-hetero- 
gamous but later has been shown to be heterogamous. As a curious 
fact, which cannot yet be explained, it is mentioned, that the sub- 
compactum-type (see my paper 1920, p. 294) so far has almost only 
been formed by the segregation in B-series (not in C- or A-series). 
11. The researches continue in a large measure. For fur- 
ther elucidating of the question of heterogamy it is especially proposed 
to make reciprocal crosses between the normal type (AA) and its 
speltoid-mutant (aa), with the intention of introducing a in a greater 
measure from the male or from the female side and thus intentionally 
creating Aa (C-series) and aA (B-series). In this manner the hypothe- 
sis of heterogamy may be definitively verified (Chapter II, H). 
ZITIERTE LITERATUR. 
1. BATESON, W. 1913. Problems of genetics. Newhaven, London, Oxford. 
2. Baresox, W, und SUTTON, Ipa. 1919. Double flowers and sex-linkage in 
Begonia. Journal of Genetics, Bd. 8, S. 199—207. 
