268 



The Journal of Heredity 



Wichura, no more than most of the 

 other hybridists of his day, paid atten- 

 tion to the crossing of characters as 

 such, he remarks upon the evidence of 

 individual characters being inherited as 

 such: "It was of interest," he says 

 (p. 27), "to observe how the unusual 

 narrowness of the leaves in the experi- 

 ment, utilizing Salix purpurea X vimina- 

 lis, remained still recognizable in the 

 following generation; a proof that, 

 even in hybrid fertilization, individual 

 characteristics of the parent plants can 

 be inherited." (Italics inserted.) 



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 (p. 40): "Not 

 only in the reproductive organs, but 

 also in their vegetative behavior, hybrids 

 show many phenomena whereby they 

 are more or less strikingly distinguished 

 from true species. According to the 

 corroborating observations of Koelreuter 

 and Gartner, a larger part of the 

 hybrids obtained by them by hand 

 crossing, were distinguished by luxuri- 

 ance 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 with- 

 stand cold longer, and had more abund- 

 ant, larger and earlier flowers than the 

 parents. . . . Among the willow 

 hybrids, similar phenomena occur, but 

 the examples of luxuriant growth by 

 no means constitute the rule." 



Wichura further observed that: 

 "Even the most sterile hybrids fall 

 behind the parents in their productive- 

 ness. A certain deficiency in the parts 

 set aside for reproduction must therefore 

 also occur with them, and 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 to say, in order to express 

 the relationship correctly, that in the 

 case of very vigorous hybrids the weak- 



ness of the sexual parts brings out an 

 increased development of the vegetative 

 growth, whereas it is not the case with 

 others which are too weak for such a 

 reaction" (meaning crosses between 

 too distant species) (p. 43). 



Wichura concluded from his observa- 

 tions that hybrids were intermediate in 

 respect to the differing parental char- 

 acters. Cases of dominance do not 

 seem to have come under his hand. 

 "Among the numerous artificial and 

 natural willow hybrids observed by me," 

 he says, "I have throughout verified 

 but one apparent exception to the 

 principle of intermediateness. 

 Even the time of flowering of hybrids 

 holds the mean between the time of 

 flowering of the two parents" (p. 47). 

 "The leaf -form of Salix caprea X 

 viminalis, for example, holds so com- 

 pletely the mean between the linear- 

 lanceolate leaves of 5. viminalis and the 

 round-ovate leaves of 5. caprea, that 

 they in fact appear to represent the 

 mathematical mean between the curves 

 for the outlines of paternal and the 

 maternal leaves" (p. 47). With regard 

 to what we should call absence of 

 dominance, he has to say (p. 50) : "As 

 rich in species as the genus of the 

 willows is, and as numerous combina- 

 tions of hybrid fertilizations as it has to 

 show, nevertheless I have never yet 

 verified anything of a preponderant 

 influence in any one of its species, but 

 rather always found that their hybrids 

 always hold the mean between the 

 constant characters of the parents" ; and 

 again (p. 86): "In hybrid fertilization, 

 if unlike factors unite, there arises an 

 intermediate formation, etc." 



The latter passage appears to be the 

 first occasion where the term "factor" 

 has been used in the literature of plant 

 breeding, although here the factors 

 referred to are the parents as a whole 

 which participate in the cross, and not 

 the character-forming elements of those 

 parents. His general conclusion is (p. 

 46): "Constant characters, through 

 which the parent species are distin- 

 guished from one another ... go 

 half over to the hybrid, so that it holds 

 the middle position between them." 



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