Dec, 1915-] 



Harris : The Beetle Bruchus. 



251 



seeds first into classes according to the number of ovules formed per 

 pod, and then sub-sorting each ovule class according to the number of 

 seeds which its pods mature, one nmy ascertain whether there is a 

 relationship between number of seeds maturing and relative numbers 

 parasitized independent of that between the number of ovules formed 

 and the incidence of the parasites. 



Diagram 6. Relationship between number of seeds matured per pod and 

 percentage frequency of Bruchus for pods with various numbers of ovules. 

 Burpee's Stringless beans. 



The results can best be presented graphically in diagrams 5 and 6. 

 Here the percentage of parasitization in pods with different numbers 

 of seeds matured is shown for pods with each class of ovules sep- 

 arately. 



The results are very irregular just as one would expect when the 

 data are split up into such numerous sub-classes. There seems, how- 

 ever, to be a distinct tendency for a higher percentage of parasitization 

 to occur in pods with larger numbers of seeds, even when the num- 

 ber of ovules is made constant by working with pods all having the 

 same number of ovules. Thus number of seeds matured seems to be 

 of independent, though probably of minor, significance in determining 

 frequency of parasitization. Further than this the analysis cannot be 

 pushed at present. 



Problem III. — Relationship between the Position of the Seed in 

 the Pod and the Percentage of Parasitized Seeds. 



At the beginning of these studies an entomological friend sug- 



