IQ22] STOUT— STERILITY Iig 



its possible relation to the production of flowers and to their 

 impotence has not been determined. 



III. Physiological 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. i 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 



