ISO 7.] Relations of Verbasca. 157 



The results of my experiments on the yellow variety of V. lychnitis 

 are given in Table 4. By a comparative examination of this Table, we have 

 the following general results : first, the fertility of the pure unions of 

 V. lychnitis, lutea exceeds that resulting from the cross-unions of 

 the latter with pollen of V. lychnitis, alba, in the proportion of 

 100 : 94. The degree of sterilisation induced by these unions, though 

 less than that resulting from the converse unions given in Table 3, is 

 nevertheless sufficient to show a sterilising influence in the conjunctions 

 of varieties of a species, characterised only by those, systematically 

 considered, trifling differences in colour — the one being white, the other 

 yellow. Secondly we have the results of unions of similarly and 

 dissimilarly coloured forms of distinct species, with V. lychnitis, lutea. 

 Thus the pollen of V. phooniccum, with purplish coloured flowers, 

 applied to the stigmas of V. lychnitis, lutea, gives an average fertility 

 of 66; the pollen of the white variety V. phceniceum, alba, gives an 

 average of 55 ; while that of the rose-coloured variety is productive of 

 the highest degree of sterilisation, giving only 49 — relatively to 100, 

 the produce of V. lychnitis i lutea by its own pollen. Mr. Darwin, on 

 the authority of Gartner, states in his " Origin of Species," that similarly 

 coloured varieties of distinct species are more fertile when crossed than 

 are the dissimilarly coloured varieties of the same species. The parti- 

 cular illustration of this point will be found in a subsequent part of this 

 paper ; I will here merely state that, in the above unions, the degrees of 

 fertility are by no means regulated by the colour affinities. Thus, we 

 have first yellow and violet, then yellow and white, and lastly yellow 

 and rose yielding a successively decreased fertility ; whereas, judging by 

 the colour affinities, the arrangement ought to have been, beginning 

 with the most fertile, yellow first with white, then with rose, and lastly 

 with violet. Secondly, with pollen of the V. blattaria, vars. alba and 

 . lutea, we see, that the V. lychnitis, lutea yields the higher degree of 

 fertility with the former : V. lychnitis, lutea, yielding with pollen of 

 V. blattaria, alba, 56, and with that of V. blattaria, lutea, 51, relatively 

 to 100, the product of fertilisation with its own pollen. Thirdly, in the 

 unions of V. lychnitis, lutea, by pollen of the yellow and white varieties 

 of V. thapsics, we find that unions of the similarly coloured flowers are 

 the more fertile. V. lychnitis, lutea, yielding with pollen of V. thapsus, 

 lutea, 46, and with the pollen of V. thapsus, alba, 39, relatively to 100, 



