1867.] 'Relations of Verbasca. 173 



lyclmitis is more potent on the stigmas of V. hlattaria, lutea, than 

 that on those of the variety alba, in the proportion of 40 to 26. 



Secondly, in mongrelism, we also find variabilities in the relative 

 sexual powers of varieties of a species, by differences in the degrees 

 of fertility resulting from their simple and reciprocal unions. Thus 

 on the calculation of V. 'plmniceum, yielding 100 seeds by ferti- 

 lisation by its own pollen, it yields with that of the variety rosea 68 

 seeds, and by that of the variety alba, 56 seeds, or nearly as 5 to 3. 

 Ln. the reciprocal unions of these varieties, we also find variabilities in 

 their converse sexual powers. For example, in the reciprocal unions 

 of V. pliceniceum and varieties, the potency of the pollen of rosea 

 relatively to that of alba on the stigmas of the normal form is nearly 

 as 5 to 4 ; whereas the pollen of the latter on the stigmas of rosea and 

 alba is as 4 to 3. This difference in the reciprocal sexual powers of 

 varieties when crossed is so regulated however by colour affinities, that 

 unlike the irregular and indefinite results of the reciprocal unions of 

 varieties of distinct species, judging by my own experience, we see 

 that the pollen of rosea is more potent on the stigmas of the normal 

 form than these of alba and so conversely, the pollen of the normal 

 form is more potent on the stigmas of rosea than on those of alba. In 

 those cases, however, in which colour differences do not come into 

 play the pollen of one variety, relatively to that of another variety 

 of the same species is so differentiated with respect to their 

 reciprocal stigmatic relations that the grade of fertility of the pure 

 unions of these varieties does not at all correspond with that of the 

 cross unions. For example, in the pure unions of varieties lutea and 

 alba of V. blattaria. the fertility of the latter exceeds that of the 

 former in about the proportions of 12 to 11 ; whereas in their converse 

 unions, lutea exceeds alba in the higher proportions of 6 to 5 ! Thus 

 in the inter- crossing of varieties of a species, as in the inter-crossing 

 of varieties of distinct species, there are converse variabilities in the 

 reciprocal sexual powers of their respective elements. 



As the facts stand then, it appears to me that in the first crosses of 

 the varieties of certain species, as in the first hybrid crosses of distinct 

 species, a variable degree of sterilisation results, and again, that the 

 relative sterilising influence is as highly intensified in the crossing of 

 undoubted varieties of certain species, as it is in the hybridising of 



