124 = Self-Incompatibility in Hermaphrodite Plants 
formed. The latter is especially involved in what Darwin calls “relative 
fertility,” the former is especially represented in “innate fertility.” An 
extreme type of loss of relative fertility is seen in self- and cross-incom- 
patibility of plants of such species as Hschscholtzia californica, Nicotiana . 
Forgetiana and Cichorium Intybus. 
In regard to the fertility of cross-bred stock we now have the state- 
ment of East and Park (1918, p. 527) that “neither Shull nor East has 
maintained that crossing increases fertility. The number of flowers and 
_ fruits is often increased but no data have appeared which indicate a 
decreased percentage of non-functional gametes.” East, who has had 
wide experience in studies of inbred and cross-bred stock, thus considers 
that increased seed production observed in certain cross-bred progeny 
is due solely to an increase in the number of sex organs. If this be true 
it appears that heterosis, at least in species in which no compatibilities 
are already in evidence, does not influence compatibilities of sex organs 
and does not raise relative fertility, a conclusion fully reached by the 
more recent report by Jones (1918). 
One may well hesitate therefore before assuming that any observed 
case of decreased productivity in selfed stock involves an actual loss in 
relative fertility. Such cases may involve solely the number of sex 
organs produced and the perfection of their development, as appears to 
be the condition in certain inbred strains of corn. 
At the present time there is no direct or even conclusive indirect 
evidence that physiological incompatibility with selective fertilization 
(at least selective for definite hereditary units) and variations in relative 
fertilities arise in a species as a direct result of inbreeding and repeated 
self-fertilization. There is therefore some question regarding the validity 
of the old doctrine that there is a tendency inherent in hermaphrodites 
for the sex organs to be non-functional together simply because they 
are produced by a single individual and that foreign pollen is naturally 
prepotent. The accumulation of evidence that inbreeding is not neces- 
sarily injurious has lead to the view that decreased vegetative and 
reproductive vigour in inbred stock is due to an inherently weak 
constitution existing before inbreeding was begun (see especially 
Jones, 1918). This of course still leaves the question open as to the 
sources and causes of the cases of weak constitution which do appear 19 
all sorts of species. | 
A question of special consideration is whether inbreeding and self- 
fertilization in species (homomorphic) in which incompatibilities are 
already in evidence lead to an increase of incompatibilities. Accor i 
