1867.] Relations of Ycrhasca. 167 



varieties of a species presenting three, or at least two, of the primary 

 colours with intermediate shades irrespective of the white. The latter 

 being rather unsatisfactory from its similar relations to the primary 

 colours, though in such instances as the above of the purplish-violet, 

 rose and white, in which we have secondary colours forming inter- 

 mediate steps between the primary and white, by a gradual dilution 

 of the colouring principle, we find that the white, agreeably to the 

 above views, form less fertile conjunctions with the violet than the 

 rose-coloured flowers. Before passing from this point of my subject, 

 I will now only add that I have thought these indications of a tangi- 

 ble law, co-relating and regulating the sexual functions of varieties 

 when crossed — dim though they as yet undoubtedly are— worth notic- 

 ing, as we are as yet in utter ignorance of any thing like definite or 

 specific laws in these phenomena, the results being considered as most 

 capricious and uncertain. 



Gartner's second proposition is, that in the hybridism of differ- 

 ently coloured varieties of distinct species of Yerbasca, the con- 

 junctions of the similarly coloured flowers are more fertile than these 

 of dissimilarly coloured flowers. For example Gartner shows* that 

 on the calculation of V. lychnitisjfl. alba, yielding with its own pollen 

 1.000 seeds, it yields when fertilised with the pollen of V. blaltaria 

 fl. alba, 0.622 seeds, and with that of V. blattaria, ,//. hdea, only 0.438, 

 so that the similarly coloured unions of tlie.^c species are more fertile 

 than the dissimilarly coloured unions in the proportion of 3 to 2. Let 

 us now see then in how far this law of the differences in the fertility 

 of the homochromatic relatively to the heterochromatic unions, is 

 borne out in the case of my own experiments as given in the preced- 

 ing Tables. And here again, for the sake of clearness, and facility of 

 reference, I will restate them in a tabular form, and show as clearly 

 as possible the differences in the relative fertility of the homochromatic 

 and the heterochromatic unions, in each case, by making calculations 

 from an assumed 100 seeds produced by the more fertile of the two 

 unions compared. The results may be conveniently arranged under 

 three heads ; thus, first, the heterochromatic unions, or those in 

 which the unions of differently coloured flo.wers are the more fertile: 

 second, the homochromatic unions, or those in which similarly colour- 

 * Yersuche uber die Bastarderzeugunj, 1849, section 216. 



