Phenomena and Problems of Self -Sterility . 203 
bG). (4) Plants sterile with B, fertile with (i (written Bg). It was 
found that these four classes were nearly equal numerically; the 
actual numbers were 16 bg, 16 bG, 14 Bg, 14 BG. 
Let us now assume 1 that the genetic constitution of the plant 
B can be written Bbgg: the presence of the factor B renders the 
plant self-sterile (whatever characters its gametes may carry): 
similarly G would have the formula bbGg ; G being another inhibitory 
factor distinct from B but alike causing self-sterility in the plants 
that carry it. 2 B produces gametes of two kinds, bg and Bg : G 
produces gametes bg and bG. The fertilisation of B by G or vice 
versa results in the production of four kinds of offspring in equal 
numbers; viz., bbgg, bbGg, Bbgg and BbGg : these are of the types 
bg, bG, Bg and BG respectively, as tested by crosses with B and G. 
This Mendelian theory is on the whole consistent with the 
results of the other experiments, and it may be accepted as a crude 
account of the phenomena, although there are certain obvious 
objections to it in this simple form. 
VI1.—Criticisms of Correns’ Theory. 
The first criticism that can be made is to point out the numerous 
irregularities in reaction of one and the same plant to the same 
repeated pollination test, and the great difficulties of classification 
of the results. The second difficulty lies in the fact that the plants 
of the type bg are not self-fertile, though they lack both inhibitors: 
if it be assumed (as indeed is necessary for other reasons) that the 
self-sterility of the bg plants is due to their possession of a number 
of other inhibitors H, jf, K . . . . , so that their true formula would 
be of the nature of bbggHhjfjKk . . . . , this raises a new difficulty 
as follows. Let the formula of B be BbggHli and of G be bbGghh : 
then their offspring will be found in the following table:— 
BgH 
Bgh 
bgH 
bgh 
bGh 
i 
bGh 
ii 
bGh 
iii 
bGh 
iv 
BgH 
Bgh 
bgH 
bgh 
bgli 
V 
bgh 
vi 
bgh 
vii 
bgh 
viii 
Of these eight classes of offspring Nos. i, ii, and iii will be 
sterile when pollinated from B and G ; Nos. v, vi and vii will be 
1 The notation used here is that most in favour among students of 
heredity in this country, and differs slightly from that employed by Correns. 
2 Since plants containing the same inhibitory factor are sterile inter se, it 
is clear that homozygotes of the type BB and GG cannot occur. 
