FERTILITY OF VARIETIES 325 



of crossing with other varieties which had originated in a 

 like manner. 



I have as yet spoken as if the varieties of the same species 

 were invariably fertile when intercrossed. But it is im- 

 possible to resist the evidence of the existence of a certain 

 amount of sterility in the few following cases, which I will 

 briefly abstract. The evidence is at least as good as that 

 from which we believe in the sterility of a multitude of spe- 

 cies. The evidence is, also, derived from hostile witnesses, 

 who in all other cases consider fertility and sterility as safe 

 criterions of specific distinction. Gartner kept during sev- 

 eral years a dwarf kind of maize with yellow seeds, and a 

 tall variety with red seeds growing near each other in his 

 garden ; and although these plants have separated sexes, they 

 never naturally crossed. He then fertilised thirteen flowers 

 of the one kind with pollen of the other; but only a single 

 head produced any seed, and this one head produced only 

 five grains. Manipulation in this case could not have been 

 injurious, as the plants have separated sexes. No one, I 

 believe, has suspected that these varieties of maize are dis- 

 tinct species; and it is important to notice that the hybrid 

 plants thus raised were themselves perfectly fertile; so that 

 even Gartner did not venture to consider the two varieties 

 as specifically different. 



Girou de Buzareingues crossed three varieties of gourd, 

 which like the maize has separated sexes, and he asserts 

 that their mutual fertilisation is by so much the 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 classifica- 

 tion by the test of infertility, as varieties, and Naudin has 

 come to the same conclusion. 



The following case is far more remarkable, and seems 

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

 ber of experiments made during many years on nine species 

 of Verbascum, by so good an observer and so hostile a wit- 

 ness 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 varieties of one species are crossed 



