106 



CAUSES WHICH CHECK 



Chap. XVI 



his 



In one instance he gives I5 the following details ■ but T 



degr< 



his crosses, always compares the maximum number obtained from a cross 

 with the average number naturally given by the pure mother-plant The 

 white variety of V. lychnitis, naturally fertilised by its own pollen gave 

 from an average of twelve capsules ninety-six good seeds in each • whilst 

 twenty flowers fertilised with pollen from the yellow variety of this same 

 species, gave as the maximum only eighty-nine good seed ; so that we "have 

 the proportion of 1000 to 908, according to Gartner's usual scale. I should 

 have thought it possible that so small a difference in fertility might have 

 been accounted for by the evil effects of the necessary castration ; but 

 Gartner shows that the white variety of V. lychnitis, when fertilised first 

 by the white variety of V. blattaria, and then by the yellow variety of 

 this species, yielded seed in the proportion of 622 to 438; and in both 

 these cases castration was performed. Now the sterility which results 

 from the crossing of the differently coloured varieties of the same species, 

 is fully as great as that which occurs in many cases when distinct species 

 are crossed. Unfortunately Gartner compared the results of the first 

 unions alone, and not the sterility of the two sets of hybrids produced 

 from the white variety of V. lychnitis when fertilised by the white and 

 yellow varieties of V. blattaria, for it is probable that they would have 

 differed in this respect. 



J. Scott has given me the results of a series of experiments on 

 Verbascum, made by him in the Botanic Gardens of Edinburgh. He re- 

 peated some of Gartner's experiments on distinct species, but obtained only 

 fluctuating results ; some confirmatory, but the greater number contradic- 

 tory ; nevertheless these seem hardly sufficient to overthrow the conclu- 

 sions arrived at by Gartner from experiments tried on a much larger scale. 



Mr 



In the 



Mr 



unions between similarly and dissimilarly-coloured varieties of the same 

 species. Thus he fertilised six flowers of the yellow variety of V. lychnitis 

 by its own pollen, and obtained six capsules, and calling, for the sake of 

 having a standard of comparison, the average number of good seed in 

 each one hundred, he found that this same yellow variety, when fertilised 

 by the white variety, yielded from seven capsules an average of ninety-four 



On the same principle, the white variety of V. lychnitis by its own 



seed. 



^psules) 



(only two capsules) 



(eight capsules) 



show variety (eight 

 The yellow variety 



Lastly, the white variety of V. blattaria by its own pollen (eight capsules), 

 and by that of the yellow variety (five capsules), yielded seed in the pro- 

 portion of 100 to 79. So that in every case the unions of dissimilarly- 

 coloured varieties of the same species were less fertile than the unions of 

 similarly-coloured varieties ; when all the cases are grouped together, the 

 difference of fertility is as 86 to 100. Some additional trials were made, 

 and altogether thirty-six similarly-coloured unions yielded thirty-five good 



15 ' Bastarderzeugung,' s. 216. 



