72 H. NILSSON-EHLE 

small proportion. This aberration is in the first line, as already shown 
in my paper 1917, caused by partial elimination of male speltoid-ga- 
metes from fertilization. Some further evidence of this elimination of 
speltoid-pollen are here given p. 29—30. In consequence of this eli- 
mination the number of mutant individuals decreases, and the number 
of normal plants increases in relation to the heterozygotes (see scheme 
III, p. 28). Those speltoid-series, in which only this complication is 
met with, are named A-series. The speltoid-series described in my 
first publication on this subject (1917) belong mostly to this category 
(Chapter II). In this paper some other such speltoids are mentioned 
(Chapter VII). 
2. In other speltoid-series, originated from other original speltoid- 
heterozygotes there must be another complication present. The elimi- 
nation of male speltoid-gametes occurs here also, but can not alone 
be responsible for the aberrant numerical proportions. In some 
series, named B-series, (tab. 3—9 and tab. 4, p. 295 in my paper 
1920) the number of normal plants compared with the heterozygotes 
is not increased as in the A-series but, conversely, largely decreased 
to */,—"/, of the heterozygotes. This small proportion of normal plants 
occurs in these series everywhere and quite regularly and is not com- 
pensated for through any increase of speltoid-homozygotes, which on 
the contrary are still more scarce in these series than in the A-series 
(Chapter III, A). 
3. In a third type of speltoid-series, named C-series (tab. 10—12 
and tab. 2, p. 290, tab. 3, p. 293 in my paper 1920) the normal plants, 
curiously enough, are more numerous than the heterozygotes. Also 
in these series the speltoid-homozygotes are very scarce (Chapter III, 
B). The speltoids of B- and C-type arise independently of each other 
in normal wheat (Chapter III, C). Yet the C-type in some cases (see 
my paper 1920, tab. 2, nos. 1920—562, 570, 572, 581) is suddenly con- 
verted into the B-type (Chapter III, D). 
4. This very apparent conversion in connexion with the few pre- 
liminary results of reciprocal crosses (Chapter III, E) and of a B- 
series Tab. 13), where the speltoid-character was introduced in the 
heterozygote by an ovule (Chapter III, F) has led to the suggestion 
or working-hypothesis, that in the B- and C-series besides elimination 
of male speltoid-gametes (A = normal gametes; a — speltoid-gametes) 
partial heterogamy occurs, that is a differential distribution of the A- 
and a-allelomorph to ovules and pollen, according as A in the diploid 
cell is introduced by an ovule (Aa) or by a pollencell (aA), as already 
