BIOTYPES AND HYBRIDS. 51 



it. The greatest frequency in any pedigree was 1 in nearly 18, and the 

 least frequency was 1 in 25.* 



I take the fact that the reciprocal crosses give similar ratios to indicate 

 that the heegeri type of capsule is dependent upon something carried by the 

 germ-cells, and can not be a pathological condition transmissible from 

 mother to offspring somatically, a possibility which might account for 

 apparent heritability of characters in a self -fertilized line, but could not 

 well account for equal results in reciprocal crosses. Normal Mendelian 

 phenomena are believed to rest pretty securely on the method of formation 

 of the chromosomes during the reduction division, but no scheme of 

 behavior occurs to me which would result in the production of a heegeri 

 homozygote in only 1 individual in 23. 



It is conceivable that the union of heegeri germ-cells in the hybrids forms 

 a less successful combination than that into which the B. burs a-pas torts 

 determiner enters, and that therefore fewer successful zygotes are formed 

 by such unions, and it is also conceivable that only a small percentage of 

 the B. heegeri succeeded in reaching sexual maturity, since in each of these 

 families a considerable number of individuals failed to fruit, but the assump- 

 tion that every individual that failed to seed was a B. heegeri would not 

 nearly bring that form up to one -fourth of the entire progeny. There was 

 no evidence in my cultures that B. heegeri is in any way inferior to B. 

 bursa-pastoris or that it is any less likely to mature; neither have I observed 

 any indication of the material lessening of fertility which would obtain if 

 almost all of the heegeri homozygotes should fail in the initial stages of 

 development. 



*Dr. Correns tells me that he also made the cross between Bursa bursa-pastoris and 

 B. heegeri several years ago and likewise found a deficiency in the number of specimens 

 having the heegeri type of capsule, but as his numbers were small he considered the 

 deficiency due alone to the inadequate numbers. 



