The Mode of Inheritance of Semi-Sterility in the Offspring of Certain Hybrid Plants. 321 



If ten per cent or so of the Velvet and Yokohama ovules abort 

 from lack of food or crowding, and few of the hybrid ovules abort from 

 this reason, but 50 per cent of them abort in the bud, we can see why 

 the average number of good seeds in the hybrid should be more than 

 half of that of the Velvet bean. The average total number of ovules 

 per pod of one Velvet plant was 5'6, that of the one Yokohama plant 

 in wliich they were counted was 6'0, and those of two Fi liyl)rid plants 

 were 6'2 and 6"1, respectively. Hence the plants start with approxi- 

 mately equal numbers of ovules per pod. The average number of seeds, 

 good and bad, in one Velvet plant was 5"Ü, in one Yokohama plant 



Fig. 1.3. Median section of fertile ovule 

 from a flower of the first generation of the 



Velvet by Cliina cross. 



Fig. 14. Slightly oblique section of sterile 



ovule from the same ovary as the fertile 



ovule shown in Fig. 13. 



5-0, and in two VY" hybrids 3-3 and 3-3. On the hypothesis that .50 

 per cent of the embryo -sacs abort in the hybrid, we should expect a 

 number between 2'5 and 3'1 for its average number of seeds, unless 

 some ovaries uith many aborted embryo-sacs drop when young, which 

 doubtless happens. 



Velvet by China.— The pods of the 10 hybrid plants (Fig. 12) 

 resembled those of the first generations of the other three crosses. 

 Microtome sections of the young ovaries of 18 flowers from one raceme 

 showed that, of the 99 ovules, .50 had complete embryo -sacs nearly 

 filling the nucellus (Fig. 13); while 49 ovules, though full -sized, had 

 either quite aborted embryo-sacs, the nucellus being a uniformly cellular 

 mass (Fig. 14), in which, however, the remains of the aborted megaspore 



Induktive Abstainmungs- und Vererbungslehre. XU. 23 



