1922] STOUT—STERILITY II3 
many were visited daily), and pollen from fully dehiscent stamens 
in liberal amounts was placed on pistils of all freshly opened 
flowers. After the cyclic modification of self-compatibility was 
recognized, frequent cross-pollinations were made to test the 
functional power of pistils and stamens during the periods of self- 
incompatibility preceding and following the period of mid-bloom. 
The potency of the pollen has been studied by germination tests, 
and a cytological study of the phenomena of pollen tube growth 
and fertilization is under way. 
Sterility in Brassica pekinensis and B. chinensis 
Three distinct and quite different types of sterility are in 
evidence during the period of bloom in both these species. 
I. One type is to be classed in general with impotence (Stout 
12), but here two very distinct types of impotence may be observed. 
These may be described as (1) flower abortion of the first flowers, 
and (2) arrested development of the last flowers that start to form. 
IT. In some plants of both species, axial proliferations develop 
from the pistils of many flowers, and the pistils of such flowers are . 
functionless in respect to fruit production. 
III. Among the flowers that open fully and are capable of 
functioning in certain relations, various grades of incompatibilities 
are in evidence, and self-compatibility whenever present is most 
strong during’ the period of mid-bloom. 
I. IMPorTreENCE 
(t) FLOWER ABorTION.—Frequently in Brassica pekinensis the 
first flowers on the main stalk and often also the first flowers on 
laterals are completely aborted. The flower buds remain small and 
do not open, but soon become dead and black. A rather character- 
istic case of flower abortion is shown in fig. 1, which is of a pot 
grown plant of B. pekinensis blooming in February. Nearly forty 
of the first flowers of the main branch aborted, after which the 
flowers were completely formed, normal in appearance, and fully 
capable of functioning in certain fertilizations. The uppermost 
lateral branch coming into bloom later than the main axis had only 
five flowers that aborted, and the next lower lateral had no aborted 
