Ig12] STEVENS—HETEROSTYLOUS PLANTS 279 
and trimorphic genera in a series of papers read before the Lin- 
nean Society during the years 1862-1868. In these early papers 
DARWIN (6-10) calls attention to the fact that the morphological 
differences in the flowers constitute a device by which cross polli- 
nation is favored, and that these differences in form are associated 
with physiological differences which affect their fertility, so that 
a flower of either form is more likely to be fully fertilized when 
pollinated from a flower of the other form (‘legitimate pollination ”’) 
than when pollinated from a flower of the same form (‘illegitimate 
pollination”). He also describes the offspring of illegitimate 
unions and points out that they differ from normal plants and 
have what he calls a ‘‘hybrid-like” nature. 
DarRWIN afterward collected these papers and published them 
in a “connected and corrected form, together with new matter” 
in The different forms of flowers in plants of the same species, which 
contains also an account of the literature on the subject up to the 
date of its publication (1877). Only three of the writers whom he 
mentions, HILDEBRAND, Scorr, and MULLER, tréat heterostyly as 
anything more than a mere difference in form or at most a device 
to favor cross pollination. 
HILDEBRAND, who first used the term “‘heterostyled,” was also 
the first to investigate the inheritance of heterostyly. In his first 
paper (18) he describes experiments on the illegitimate fertilization 
of Linum perenne and Primula sinensis. The illegitimately pol- 
linated flowers of Linum were uniformly sterile. In Primula, 
however, all the illegitimately pollinated flowers developed cap- 
sules, which contained an average of 18 seeds, about two-fifths the 
number found in the capsules of legitimately pollinated flowers. 
HILDEBRAND planted the seeds thus produced, and found that while 
the seeds of either form legitimately fertilized produce long-styled 
and short-styled forms in about equal numbers, the seeds from 
illegitimate unions tend to reproduce the parent form. Seeds from 
illegitimate unions of long-styled plants, however, tend to transmit 
the parent form more truly than those of the short-styled. This 
conclusion was accepted by DARWIN, but the results he later 
obtained from similar experiments with Primula sinensis do not 
agree very closely with those of HILDEBRAND. 
