190 PLANT HYBRIDIZATION BEFORE MENDEL 



hybrids of varieties, and of variety-like species. When it occurs 

 with other species-hybrids, it appears to be limited to those cases 

 where one species has exercised a predominant influence in the 

 hybrid fertilization, {ib.^ p. 231.) 



Regarding "variability" in hybrids in general, Nageli remarks : 



"Variability of the hybrids, that is to say, the diversity of forms which 

 belong to the same generation, and their behavior on propagation once 

 or many times by self-fertilization, form two points in the study of 

 hybridization which are still least ascertained, and which the least ap- 

 pear to be subjected to fast rules." {ib., p. 231.) 



"Among the species-hybrids, there are also some which already in the 

 first generation show a noticeable variability. These are especially those 

 which are derived from very nearly related species, as the hybrid of 

 Lychnis diurna Sibth. X Lychnis vespertina Sibth. The least variability is 

 found as a rule in the hybrids of those parent species which possess a 

 slender mutual relationship." {ib., p. 232.) 



In the case of allied species, each of which has similar variety 

 types, according to Nageli, the mutually similar types cross more 

 readily than the others ; e.g., Verbascum blattaria Linn, and Ver- 

 bascum lychnitis Linn, have both yellow and white-flowered vari- 

 eties. The white-flowered V. blattaria crosses more readily with 

 the white-flowered V. lychnitis^ and vice-versa, and the same holds 

 good as to the number of hybrid seeds produced. 



The following statement appears to be the nearest approach 

 to an observation of anything like a "Mendelian" character to be 

 found in Niigeli's writings: 



"when the hybrids are self-fertilized, the variability increases so much 

 the more in the second and succeeding generations, the more it was lack- 

 ing in the first, and indeed the farther apart the parental forms lie from 

 one another, the more certainly three different varieties spring up, one 

 which corresponds to the original [i.e., hybrid] type, and the two others 

 which are more like the parental forms." {ib., p. 230.) 



Despite the existence of correspondence between Mendel and 

 Nageli, the latter does not so much as mention Mendel's Hiera- 

 cium crosses, even in the somewhat extensive paper of twenty- 

 nine pages, of March 10, 1866, "Die systematische Behandlung 

 der Hieracien, riicksichtlich der Mittelformen" (4h). 



A further epitomization of rules or conclusions regarding hy- 

 brids appears, in the form of seven summarized statements and 

 commentaries thereupon, in Nageli's paper (4f). 



1. Nageli concludes that the hybrid in all its parts is an en- 

 tirely normal phenomenon, and is distinguished in no manner 



