PLANT HYBRIDIZATION BEFORE MENDEL 185 



concerning the manner in which the characters of the parents are carried 

 over to the offspring." {ib.) 



Concerning the question whether hybridization could be used 



to reveal the then much-disputed difference between "species" and 



"variety," Nageli concludes that between species and varieties 



there exists no essential difference, in characters which either the 



external form, the internal structure, or the chemical composition 



exhibits, but that there is simply a gradual intergradation between 



the two. 



"If we compare species and varieties with regard to sexual affinity, we 

 find no boundary which divides them. In general, the relationship is, of 

 course, greater between varieties and lesser between species." (4c, p. 200.) 



This being the case, there can be no point in making the be- 

 havior of hybrids determine whether the parents of the cross 

 were "species," or "varieties," and yet, as Nageli remarks: 



"By far the most numerous and the most important investigations on 

 hybridization have been carried on by decided adherents to specific 

 fixity." 



Elsewhere Nageli refers to the origin of species and varieties 



in the following words : 



"For, when it becomes apparent that varieties are not the consequence 

 of external influences, but are brought a^bout through inner causes, then 

 the difference in principle between specific and varietal, constant and 

 variable characters, is removed. One must then assume, from the tendency 

 to vary in the plant independently from without, that it is the specific 

 nature itself which determines variety formation. Between species and 

 variety there exists then a causal relation, and the relation finds its 

 logical expression in the principle that the species is nothing but a fur- 

 ther developed variety." (4a, p. 104.) 



"The formation of more or less constant varieties or races is not the 

 consequence and the expression of outer agencies, but is brought about 

 through inner causes." {ib., p. 105.) 



After enumerating the list of experimenters and investigators 



in the field of hybridization, he says : 



"if, in spite of these numerous experiments, no greater agreement 

 with respect to hybrid-formation in the plant kingdom prevails, the 

 reason may reside in various circumstances . . . Proceeding from the un- 

 alterableness of ^pecies, the endeavor is above all to determine the 

 difference between species-hybrid and variety-hybrid — a difference which 

 in reality does not exist." (4c, p. 89.) 



In this paragraph, Nageli briefly states the unfortunate situa- 

 tion into which the study of hybrids had fallen. In a word, the 

 whole matter of the study of hybridization was largely used as a 

 means for determining degrees of distinction between species. 



