1922] STOUT—STERILITY IIg 
its possible relation to the production of flowers and to their 
impotence has not been determined. 
III. PuHyYsIoLOGICAL INCOMPATIBILITY 
During the phase when the flowers are completely developed, 
many flowers are produced that are capable of producing pods and 
seeds. In general the plants produce such flowers in abundance, 
in succession for a period of about twenty days, and with con- 
tinuous and rather rapid elongation of branches (cf. fig. 1 with 4 and 
6). A free and indiscriminate functioning of the organs in seed 
production, however, is decidedly limited by incompatibilities in 
fertilization. 
SELF-INCOMPATIBLE PLANTS.—Plants may be completely self- 
incompatible throughout, as was the case for the plant shown in 
fig. 4. The first six flowers on the main branch aborted, but the 
very first flowers on the three uppermost laterals were normal. 
A few flowers at the ends of the branches failed to develop. In all, 
about seventy flowers on the main branch, forty on each of the first 
and second laterals, and fifty on the third lateral were capable of 
functioning. Three lower branches, which bore together about 
one hundred normal flowers and were like the third lateral in general 
appearance, were not included in the photograph. This plant grew 
in isolation in a greenhouse, and self-pollinations were made by 
hand at least three times a week throughout the period of bloom. 
At least two hundred flowers were carefully self-pollinated, but 
not a pod resulted. The pods which were formed on this plant 
were all from compatible cross-pollinations. Six fine large pods 
near the base of the main stem were all from flowers that opened 
rather early; the two first flowers on the first lateral yielded fine 
pods to a cross; and large pods containing viable seeds were 
obtained by crossing some of the very last flowers to open normally 
on the main stem and on the first and second laterals. The stamens 
were apparently normal throughout the time when flowers opened 
normally; pollen from many stamens examined at different times 
was found to be plump and normal in appearance, and the use of 
pollen in certain crosses covering the entire period of normal 
bloom resulted in seeds. Such tests have been made repeatedly on 
