92 Self-Incompatibility in Hermaphrodite Plants 
This indicates most clearly, as I have pointed out above, that 
incompatibilities, and especially self-incompatibilities, are acquired, and 
may, under special conditions, give way to the original primitive condition 
of full self-fertility. The whole set of conditions favours the conception 
that compatibility depends on similarity of gametes. Acquired differ- 
ences which result in self-incompatibility have marked selective value 
only to the advantages in variability resulting from limiting sexual 
reproduction to crossing between individuals or races. 
Further evidence of variability in the relations of incompatibility 
is seen in the fact that self-fertility is more pronounced in WN. alata 
than it is in NV. Forgetiana. It is interesting to note that East and 
Park consider that these conditions and differences can be so fully 
disregarded in judging heredity that each species can be called fully 
self-sterile, and be described as homozygous for a single unit factor 
(or possibly multiple factors) solely concerned with the hereditary 
transmission of self-incompatibility. 
East and Park have made the most extensive studies of reciprocal 
crosses that have thus far been reported. Their facts show a considerable 
variation in the reciprocal relations of two individuals, but they believe 
that this is solely due to experimental error and to differences in 
maturity of the individuals, and that reciprocal matings should give the 
same results provided end-season conditions are not involved. They 
decide, therefore, that the condition of compatibility or incompatibility 
between sex organs (including the gametophytic generation) is deter- 
mined for a plant as a whole rather than for sex organs as such. This 
view is decidedly at variance with the results which Sirks, and also 
the writer have found, as noted above. 
East and Park consider that inbreeding or breeding from self-fertile 
plants increases the amount of cross-incompatibility ; the marked or 
very general cross-incompatibility of a progeny being ascribed to 
increased homozygosity. This assumption seems to have some evidence 
in its support, but it has by no means been rigorously tested and 
adequately proven. | 
The point of view of East and Park is that incompatibilities, both 
self and cross, are not fundamentally phenomena of sex differentiation, 
but are properties of plants as wholes predetermined by line stuffs. The 
emphasis is placed on a Mendelian description in terms of hereditary 
units. They recognize that characters and factors representing them 
are very generally. variable, but prefer to regard the marked variations 
in self-fertility as a “pseudo” fertility of no genetic significance and to 
