V. GRANT 71 



however, as expressed by Mayr (1942), Blair (1951), Hubendick 

 (1951), Dobzhansky (1953), Fisher (1954), and other authors, 

 is that hybridization is a rare and abnormal event which usually 

 ends with the production of a few interesting but inconsequential 

 freaks. 



No similar categorical conclusion with regard to the plant king- 

 dom can be seriously considered by botanists. That natural hy- 

 bridization has evolutionary consequences of considerable im- 

 portance was suggested in an early period by Naudin (1863), 

 Kerner (1891), Lotsy (1916), and others. Botanical studies, in 

 numerous groups of higher plants, utilizing more refined tech- 

 niques developed especially by Anderson, have amply confirmed 

 and extended the conclusion reached by the pioneer hybridolo- 

 gists that hybridization has profoundly affected the course of 

 plant evolution (cf. Anderson, 1953; Grant, 1953; Anderson and 

 Stebbins, 1954). This conclusion seems to be as true for the lower 

 vascular plants as for the seed plants (Manton, 1950; Wagner, 

 1954). 



A consideration of both the zoological evidence and the bo- 

 tanical evidence leads us to a tentative general conclusion. The 

 zoological evidence now available, accepted at its face value, sug- 

 gests that natural interspecific hybridization may have been a 

 small or even a negligible factor in the evolution of many higher 

 animals. The botanical evidence proves that natural interspecific 

 hybridization has been an important evolutionarv process in the 

 plant kingdom. 



The direct effects of natural hybridization on the species prob- 

 lem in plants are plain enough. These effects range in magnitude 

 from a slight blurring of species distinctions to the development 

 of a huge intricate syngameon in which the original species are 

 more or less lost as distinct entities. It remains to point out that 

 natural hybridization is indirectly involved in two other sources 

 of a species problem in plants. 



Sibling species, as previously noted, are a byproduct of poly- 

 ploidy; polyploids outside the experimental garden are in the 

 great majority of cases allopolyploids; and allopolyploids are the 

 polyploid derivatives of interspecific hybrids. Asexual reproduc- 



