PLANT HYBRIDIZATION BEFORE MENDEL 195 



Linn, gave 220 to 280 seeds ; the parents 600 to 800 seeds. There 

 are other hybrids, as Nageli says, which produce only ^4' i/^' 

 1/10, or 1/20 as many seeds as the parent species. This weaken- 

 ing of sexual vigor in species-hybrids, as Nageli says, also 



". . . shows itself plainly in the fact that all species-hybrids give fewer 

 seeds by self-fertilization than when pollinated by one of the parent 

 species." (4c, p. 202.) 



A question of scientific moment, is discussed by Nageli in re- 

 spect to the nature of reciprocal crosses. In most of Kolreuter's 

 and Gartner's crosses, as Nageli says, the results of the crosses 

 were so much alike that a difference in point of deviation was 

 not to be recognized. In the case of some plants, however, a 

 slight difference showed itself 



". . . more frequently in the form and color of the flowers, more seldom 

 in the form and substance of the leaves." (4c, p. 217.) 



Nageli calls attention also to the fact brought out by Gartner's 

 investigations, that in some cases, where reciprocal crosses are 

 identical, yet their progeny derived from self-fertilization show 

 differences. Gartner's cases are cited, of Digitalis purpurea X D. 

 lutea, and Dianthus pulchellus X D. arenarius, as being more 

 "variable" in their progeny than their reciprocals. What this par- 

 ticular mode of variability in the first generation may consist in 

 is not stated. 



The general state of knowledge in Nageli's time of the be- 

 havior of plants in crossing, since made clear through Mendel's 

 results, is well exemplified in his statement as follows: 



"if it is certain that in hybrid formation, in individual cases, the one 

 parental form shares more actively than the other, still the question may 

 be reasonably asked, whether the hybrid ever inherits mathematically 

 equally much from its parents ; whether the one or the other parental 

 form has not always the preponderance. This is, of course, probable, 

 but facts are still lacking which are able to decide the question in one 

 or the other direction." (4c, p. 222.) 



Mendel's work solved in part this" very problem, to the extent 

 of showing the presence of so-called "dominant" factors in the 

 one or the other parent. Nageli's paper (4b), here reviewed, was 

 read before the Royal Bavarian Academy of Sciences at Munich, 

 December 15, 1865. The preceding February 8 and March 8 of 

 the same year witnessed the reading of Mendel's paper on hybrid- 

 ization, before the Natural History Society of Briinn. In other 



