Chap. XVI. THE CROSSING OF VARIETIES. 105 



varieties of wheat differ in any important character, it seems to me very 

 improbable that the sterility resulted, as Mr. Sheriff thought, from the 

 cross, but from some quite distinct cause. Until such experiments are 

 many times repeated, it would be rash to trust them; but unfortunately 

 they have been rarely tried even once with sufficient care. 



Gartner has recorded a more remarkable and trustworthy case: he 

 fertilised thirteen panicles (and subsequently nine others) on a dwarf 

 maize bearing yellow seed 12 with pollen of a tall maize having red seed; 

 and one head alone produced good seed, only five in number. Though 

 these plants are monoecious, and therefore do not require castration, 

 yet I should have suspected some accident in the manipulation had 

 not Gartner expressly stated that he had during many years grown these 

 two varieties together, and they did not spontaneously cross; and this, 

 considering that the plants are monoecious and abound with pollen, and 

 are well known generally to cross freely, seems explicable only on the belief 

 that these two varieties are in some degree mutually infertile. The 

 hybrid plants raised from the above five seed were intermediate in struc- 

 ture, extremely variable, and perfectly fertile. 13 No one, I believe, has 

 hitherto suspected that these varieties of maize are distinct species ; but 

 had the hybrids been in the least sterile, no doubt Gartner would at once 

 have so classed them. I may here remark, that with undoubted species 

 there is not necessarily any close relation between the sterility of a first 

 cross and that of the hybrid offspring. Some species can be crossed with 

 facility, but produce utterly sterile hybrids ; others can be crossed with 

 extreme difficulty, but the hybrids when produced are moderately fertile. 

 I am not aware, however, of any instance quite like this of the maize with 

 natural species, namely, of a , first cross made with difficulty, but yielding 

 perfectly fertile hybrids. 



The following case is much more remarkable, and evidently perplexed 

 Gartner, whose strong wish it was to draw a broad line of distinction 

 between species and varieties. In the genus Verbascum, he made, during 

 eighteen years, a vast number of experiments, and crossed no less than 

 1085 flowers and counted their seeds. Many of these experiments con- 

 sisted in crossing white and yellow varieties of both V. lychnitis and V. 

 Uattaria with nine other species and their hybrids. That the white and 

 yellow flowered plants of these two species are really varieties, no one 

 has doubted; and Gartner actually raised in the case of both species 

 one variety from the seed of the other. Now in two of his works 14 he 

 distinctly asserts that crosses between similarly-coloured flowers yield 

 more seed than between dissimilarly-coloured ; so that the yellow-flowered 

 variety of either species (and conversely with the white-flowered variety), 

 when crossed with pollen of its own kind, yields more seed than when 

 crossed with that of the white variety ; and so it is when differently coloured 

 species are crossed. The general results may be seen in the Table at the 



12 ' Bastarderzeugung,' s. 87, 169. 14 ' Kenntniss der Befruchtung,' s. 

 See also the Table at the end of 137; 'Bastarderzeugung,' s. 92, 181. 

 volume. On raising the two varieties from seed 



13 ' Bastarderzeugung,' s. 87, 577. see s. 307. 



