GENETICS: E. M. EAST 
95 
AN INTERPRETATION OF SELF-STERILITY 
By E. M. East 
BUSSEY INSTITUTION. HARVARD UNIVERSITY 
Pie«ented to the Academy, December 28, 1914 
In certain hermaphroditic animals and plants, self-fertilization is 
often impossible. This gametic incompatibility has been called self- 
steriKty. In the vegetable kingdom it is known to be comparatively 
widespread; in the animal kingdom, though it may be found later to be 
characteristic of many species, as yet only the Ascidian Ciona intestin- 
alis has furnished material for study of the problem. (See Morgan,^ 
Adkins, in Morgan,^ and Fuchs.^) 
Ciona is not perfectly self-sterile. Individuals appear to vary in de- 
gree of self-sterility, though no case has yet been found where self- 
fertiHty is equal to cross-fertility. Morgan believes that there is a 
great difference in the compatibility of ova to sperm from other indi- 
viduals, though Fuchs maintains that 100% 'of segmenting eggs can be 
obtained in every cross with normal ova if a sufficiently concentrated 
sperm suspension is used. 
Fuchs has shown a chemical basis for the phenomenon by the differ- 
ence in ease of cross-fertilization after contact of ova with sperm from 
the same animal and by the variation in ease of self-fertilization after 
certain artificial changes in the chemical equilibrium of the medium 
surrounding the ova, and by this work has brought the matter of self- 
sterility in Ciona in line with that in Angiosperms as worked out by 
Jost.^ 
Jost has shown that in the plants with which he worked only short 
tubes were formed after pollination with pollen from the same plant, 
though the necessary length of pollen-tube was easily developed after 
cross-fertilization. He saw as cause of these phenomena a chemotropism 
due to the presence of 'individueller Stoffe.' Pollen was indifferent to 
' Individuals toff ' from the same plant, but was stimulated by that from 
other plants. 
To Correns^ such an explanation of self-sterility seemed too general. 
He believed that a simple interpretation would account for the results 
he had obtained from Cardamine pratensis. Two plants B and G were 
crossed reciprocally and sixty of the offspring tested by pollinating from 
the parents, on the parents and from sisters. The back crosses of (B X G) 
or (G X B) with B and with G seemed to him to indicate four equal- 
sized classes with reference to gametic compatibility: (1) plants fertile 
