Nov., 1923] 
EAST — SELF- AND CROSS-STERILITY 
469 
certain evidence gleaned from studying the behavior of the self-sterile 
plants among themselves, one is led to the belief that either the primary 
self-sterility factor exists in various allelomorphic forms each having a 
different efficacy in causing self-sterility or that secondary factors exist 
which modify this efficacy. 
This variation in the efficiency of the self-sterility factor is a peculiar 
thing. It does not mean that all plants homozygous for ff are not self- 
sterile, for this is not the case. It means only that there is a considerable 
variation in the ease or difficulty with which environmental changes can 
produce the slight indication of self-fertility which I have termed pseudo¬ 
fertility. Under normal conditions all plants of these species are wholly 
self-sterile. When grown with ordinary care either in the greenhouse or 
out of doors they produce not a single seed after selfing, for the first month 
or so of the flowering season. Later, a few seeds will sometimes be produced 
after selfing, and this pseudo-fertility appears as a response to changed 
environmental conditions more readily in some families than others. 
There has been some criticism of the use of the term pseudo-fertility. 
The critics would have it that a plant which produces any seed whatsoever 
after a self-pollination is self-fertile, no matter if it has shown complete 
self-sterility in 200 or 300 attempts at selfing under what I term normal 
conditions. The position of these critics is indefensible. It shows an 
astonishing ignorance of both genetical methods and genetical results. 
Furthermore, those who take this position are so handicapped by it that 
they can make no constructive analysis either of their own or other results 
on self-sterility, although the data yield to a very simple interpretation 
when it is understood that this pseudo-fertility is a mere environmental 
fluctuation having nothing to do with heredity. I might say in passing 
that every somatic character is affected by external conditions. In ordinary 
cases, such as flower color, one finds that he must make his records before the 
flower wilts and fades. In less common examples, like the Drosophila 
mutant having 12 legs, the individuals must be raised under extraordinary 
conditions in order to bring out the character—in this case extreme cold 
is necessary. Another example would be hair characters in the human 
race. Would these critics say that hair color could not be studied because 
a man becomes bald? Could it be maintained that I did not inherit brown 
hair, just because I do not have much of it left now, or because of the 
prospect that I will not have any left a little later? I propose to sit tight 
on this proposition against all-comers as a matter of honor. 
Speaking seriously, pseudo-fertility in the self-sterile plants with which 
I have been working is a rare occurrence; but it may be caused by any 
proper combination of circumstances which tends to make the flowers hang 
to their stems longer and which tends to make the pollen tubes grow more 
rapidly. Concretely, it is found when the plants are old and the tempera¬ 
ture is between 8o° and 90° F.; but these conditions produce more marked 
