GENETICS: E. M. EAST 
97 
at least eight different shades of color. In the F2 generation, twenty 
plants coming from two crosses between Fi plants were selected for 
experiment. Each was selfed many times and in addition 131 inter- 
crosses were attempted, from four to twelve flowers being used in each 
trial. All attempts at selfing failed, while only two attempts at crossing 
were unsuccessful. Of the 129 successful inter-crosses, all but 4 pro- 
duced full capsules, and it is probable that even this variability in ease 
of cross-fertilization was caused by attending conditions. One hundred 
and twenty other inter-crosses were made in the F2 generation, with 
three failures. 
In the F3 generation, about one hundred inter-crosses were made be- 
tween twelve plants which were the progeny of two sister F2 plants. 
Six of these attempts failed. 
In the F4 generation, fifty-eight inter-crosses were made between ten 
plants that were the daughters of two F3 plants. Fifty- three of these cross- 
fertilizations were successful. 
Back crosses also were made in considerable numbers, though not to 
the extent one might desire. Plants A, B, C and D were combined in 
four different ways and among the plants resulting from these combi- 
nations eighty-five back crosses were attempted, of which five failed. 
These facts will not fit any simple MendeHan formula similar to that 
proposed by Correns; furthermore, data from an experiment of a differ- 
ent kind appear to support Jost's idea of 'Individualstoffe' rather than 
Correns' idea of inhibitors. Pairs of plants were provided to furnish 
series of selfed and crossed flowers. The pistils of these flowers were 
fixed at regular periods after pollination, stained, sectioned and the 
pollen- tubes examined. Since the flowers on each plant had about 
the same length of pistils, curves of pollen-tube development for both 
crossing and selfing could be constructed. The pollen grains germinated 
perfectly on stigmas from the same plant, from 1200 to 2000 tubes having 
been counted in sections of single pistils. The difference between the 
development of the tubes in the selfed and the crossed styles was wholly 
one of rate of growth. The tubes in the selfed pistils developed steadily 
at a rate of about 3 mm. per twenty-four hours, with even a sHght ac- 
celeration of this rate as the tubes progressed. If the flowers were 
sufficiently long-lived, one could hardly doubt but that the tubes would 
ultimately reach the ovules, though this would not necessarily mean that 
fertilization must occur. Since the maximum fife of the flower is about 
11 days, however, the tubes never traverse over one-half of the distance 
to the ovary. On the other hand, the tubes in the crossed pistils, though. 
