i8o PLANT HYBRIDIZATION BEFORE MENDEL 



"ternary," and "quaternary" crosses, i.e., crosses (l) between two 

 species; (2) between a species and a hybrid; and (3) crosses be- 

 tween two hybrids. Besides the smaller list of Wichura's successful 

 crosses, he published a much longer one of his failures, which 

 stands as evidence both of the considerable amount of crossing- 

 work that was done, and of the scientific integrity of the experi- 

 mentor. 



Of the ordinary, or, as he calls them, "binary" crosses Wichura 

 made in all thirty-five successful crosses and combinations of 

 such (of which ten were strictly "binary," i.e., simply crosses in 

 the ordinary sense), between twenty-one different species of wil- 

 lows. 



Although, as has been stated, Wichura, similarly to most of the 

 other hybridists of his day, paid no attention to the crossing of 

 characters taken as units, he remarks upon the evidence of indi- 

 vidual characters being inherited as such : 



"It was of interest," he says (6, p. 27), "to observe how the unusual 

 narrowness of the leaves in the experiment, utilizing Salix purpurea X 

 viminalis, remained still recognizable in the following generation ; a 

 proof that even in hybrid fertilization individual characteristics of the 

 parent plants can be inherited." 



Wichura noted in willows, as others had done in other plants, 



the fact of a higher degree of sterility on the part of hybrids 



obtained between species of more distant specific relationship. The 



greater amount of vegetative vigor of hybrids was remarked upon 



by Wichura in the following words (6, p. 40) : 



"Not only in the reproductive organs, but also in their vegetative be- 

 havior, hybrids show many phenomena whereby they are more or less 

 strikingly distinguished from true species. According to the corroborating 

 observations of Kolreuter and Gartner, a larger part of the hybrids ob- 

 tained by them through hand crossing were distinguished by luxuriance 

 of growth. The plants grew to a greater height than the parents, spread 

 out farther laterally by virtue of an increased capacity for sprouting, 

 had a longer life-period, were able to withstand cold longer, and had 

 more abundant, larger, and earlier flowers than the parents. . . . Among 

 the willow hybrids, similar phenomena occur, but the example of luxu- 

 riant growth by no means constitutes the rule." 



Wichura further observed that : 



"Even the most fertile hybrids fall behind the parents in their produc- 

 tiveness. A certain deficiency in the parts set aside for reproduction must 

 therefore also occur with them, if we associate this in reverse relation 

 with the excess of their vegetative development, it stands in complete 

 harmony with the facts otherwise demonstrated. We shall therefore have 



