38 FERTILITY OF VARIETIES [Chap. IX 



less easy as their differences are greater. How far these 

 experiments may be trusted, I know not; but the forms 

 experimented on are ranked by Sageret, who mainly 

 founds his classification by the test of infertility, as 

 varieties, and Naudin has come to the same conclusion. 



Th? following case is far more remarkable, and seems 

 at first incredible; but it is the result of an astonishing 

 number of experiments made during many years on 

 nine species of Verbascum, by so good an observer and 

 so hostile a witness as Gartner: namely that the yellow 

 and white varieties when crossed produce less seed than 

 the similarly coloured varieties of the same species. 

 Moreover, he asserts that, when yellow and white varie- 

 ties of one species are crossed with yellow and white 

 varieties of a distinct species, more seed is produced 

 by the crosses between the similarly coloured flowers, 

 than between those which are differently coloured. Mr. 

 Scott also has experimented on the species and varieties 

 of Verbascum; and although unable to confirm Gart- 

 ner's results on the crossing of the distinct species, he 

 finds that the dissimilarly coloured varieties of the 

 same species yield fewer seeds, in the proportion of 86 

 to 100, than the similarly coloured varieties. Yet these 

 varieties differ in no respect except in the colour of 

 their flowers; and one variety can sometimes be raised 

 from the seed of another. 



Kolreuter, whose accuracy has been confirmed by 

 every subsequent observer, has proved the remarkable 

 fact, that one particular variety of the common tobacco 

 was more fertile than the other varieties, when crossed 

 with a widely distinct species. He experimented on 

 five forms which are commonly reputed to be varieties, 

 and which he tested by the severest trial, namely, by 



