Volume JO Number 2 



The Plant World 



a /llbagajine of ©eneral :f6otans 

 FEBRUARY, 1907 



HYBEIDS AMON^G AVlLD PLANTS. 



By ])u. D. T. MAcDoroAL. 



Nearly one per cent, of the seed-plants native to Eastern 

 North America are taken by systematists to be hybrids, or the 

 results of crosses between two species. In most instances con- 

 chisions as to the hybrid nature of a ])hnit are drawn from the 

 fact that it appears to be intermediate between the two in form 

 and intimate strncture. Oftentimes the two supposed parents 

 constitute the only members of the genus in the region. 



This is not an entirely safe method of reasoning, however, 

 since the structure of the leaves, stems, flowers and fruit are not 

 a safe index of a relationship of this kind, and the supposed 

 hybrid may be a sport or mutant coming from one of the sup- 

 posed parents alone. Whether or not two nearly related species 

 will cross with each other depends on so many delicate conditions 

 that hybridization may not l)e predicted with safety; the only 

 method on which any reliance can be put consists in actual test. 



If we suppose a plant to be a hybrid between two other 

 species Ave may obtain proof by re-making the cross with some 

 hope of (hiplicating the hybrid, although this may not always be 

 successful. Then again some hybrids show alternative inherit- 

 ance, by reason of which the progeny beginning witli the second 

 generation include a groat number of forms not resend)ling their 

 parents exactly, but showing the ancestral characters in various 



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