INTERCROSSES BETWEEN SELF-STERILE PLANTS 
E. Ma EAST 
Bussey Institution, Harvard University 
The fact that self-fertilization is practically impossible in certain 
hermaphroditic plants, although both the pollen and the ovules are 
functional in crosses, has been known since the time of K6lreuter 
(1760-1765). The oddity of the phenomenon has been a lure for al- 
most every hybridist from that time forward. As in the case of most 
other genetical problems, however, our knowledge of its cause and 
meaning remained in status quo from the time of Darwin until Men- 
delian days. Indeed when the writer began his investigations on the 
subject in 1910, the only considerable post-Darwinian work had been 
done by a zoologist (Morgan, 1904) on the self-sterile ascidian, Ciona 
intestinalis. Since 1910 botanical papers have appeared by Correns 
(1912), Compton (1913) and Stout (1916), but these investigations 
will not be discussed here, as it is proposed to treat in this paper only 
certain phases of the work carried on by the author and his associates! 
during the past seven years, leaving critical review for another place. 
For our purpose it seems essential only to present a hasty sketch of 
the subject as left by Darwin. 
In addition to the utilization of most of the previous and the con- 
temporaneous work, Darwin (1876) carried out several investigations 
of his own on the five self-sterile species, Eschscholtzia californica, 
Abutilon darwinti, Senecio cruentus, Reseda odorata and Reseda lutea. 
Darwin’s first important result was that the expression of self- 
sterility in Eschscholtzia californica and Abutilon darwinti was influ- 
enced by changes in external conditions. Six generations of Esch- 
scholtzia californica had been found to be completely sterile in southern 
Brazil by Fritz Miiller (1868, 1873). As English plants were self- 
fertile, Darwin obtained from Miiller seed of Brazilian plants of known 
self-sterility. The plants which they produced in England, while 
not wholly self-fertile, tended toward self-fertility, which fact Darwin 
attributed to the lower English temperature. A second generation of 
seedlings proved to be still more self-fertile. Conversely, seed of 
English stock was somewhat self-sterile the first season and one plant 
' The author desires to make grateful acknowledgment to Dr. O. E. White and 
Dr. J. B. Park for their painstaking aid in this work. Without it, the numerous 
experiments undertaken could not have been completed. 
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