WICIITJIIA ON HYBRIDS. 



77 



year down to the ground, and never bears blossoms. S. purpurea 

 with confluent stamens, and S. viminalis with free stamens, form 

 a hybrid with very irregular pollen. On the contrary, the pollen 

 of IS. (caprea+viminalis), both of the parents of which have free 

 stamens, has much more regular pollen. The more different the 

 parent species, the more imperfect the hybrids. Examples might, 

 moreover, be adduced of more complicated hybrids in confirmation 

 of this position. 



It follows that those species only can combine to form hybrids 

 which agree in a proportionally large number of peculiarities and 

 the relative biological conditions, which accords with the fact that 

 only cognate species or nearly allied genera can combine. 



"Were it necessary to prove by experiment that every species, 

 in order to maintain itself in certain vital conditions, requires all 

 the peculiarities with which it is endowed, one could think of 

 nothing more appropriate than hybridizing, which calls into action 

 in a weak and impaired intermediate condition all the constant 

 differences of the parents. "Were the hybrid as vivid and vigorous 

 it would be a contradiction to this hypothesis. 



The constantly increasing sterility in hybrids, and their dying 

 out when fertilized with their own pollen, belongs probably to 

 another class of phenomena. It is notorious that families which 

 have the seeds of disease in them, and yet intermarry, die out 

 after some generations ; and the raisers of varieties are well aware 

 that all abnormal peculiarities in plants and animals increase, if 

 attention is paid to them in successive generations, so that propa- 

 gation is confined to these abnormal individuals. If a hybrid is 

 fertilized for successive generations with its own pollen, indi- 

 viduals come together which have the same weak point, viz. that 

 of reproduction. The increase of weakness and sterility, and the 

 rapid dying out of hybrids by continual impregnation with their 

 own pollen, agrees perfectly with the above-mentioned circum- 

 stances. This is exactly Darwin's view of interbreeding causing 

 sterility in successive generations. 



JEgilops speltceformis, Jordan ( $ ( $ ^2. ovata, L. + Triticum 

 vulgar e, L.) + $ T. vulgar e) is an apparent exception to this rule. 

 Esprit Eabre raised in 1858, from a spontaneous hybrid (JEgilops 

 ovata + Triticum vulgar e), JEgilops triticoides, Eequien, and at a 

 later period Godron bred an artificial hybrid from the same 

 parents, and fertilized this again with the pollen of Triticum vul- 

 gar e, which is now commonly multiplied in gardens, under the 

 same of JEgilops spelt&formis, while the primary hybrid is very 



