Chap. XVL THE CROSSING OF VARIETIES. 83 



yellow seecl u with pollen of a tall maize having red seed; and one 

 head alone produced good seed, bnt 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 seeds were intermediate in structure, extremely variable, and 

 perfectly fertile. 12 In like manner Prof. Hildebrand 13 could not 

 succeed in fertilising the female flowers of a plant bearing brown 

 grains with pollen from a certain kind bearing yellow grains ; 

 although other flowers on the same plant, which were fertilised 

 with their own pollen, yielded good seed. No one, I believe, even 

 suspects 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, namely, of a 

 first cross made with difficulty, but yielding perfectly fertile hybrids. 14 

 The following case is much more remarkable, and evidently per- 

 plexed 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 consisted in crossing white and yellow varieties 

 of both V. lychnitis and V. blattaria 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 15 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 tbe white-flowered variety), when 

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



11 ' Bastarderzeugung,' s. 87, 169. varieties of wheat became sterile in 

 See also the Table at the end of the fourth generation ; but he now 

 volume. admits (' Improvement of the Cereals,' 



12 < Bastarderzeugung,' s. 87, 577. 1873) that this was an error. 



13 <Bot. Zeitung,' 1868, p. 327. 15 ' Kenntniss der Befruchtung,' s. 



14 Mr. Shirreff formerly thought 137 ; ' Bastarderzeugung,' s. 92, 181. 

 C Gard. Chron.,' 1858, p. 771) that the On raising the two varieties from seed, 

 offspring from a cross between certain see s. 307. 



