PLANT HYBRIDIZATION BEFORE MENDEL 189 



characters go over to the hybrid the more unchanged, the more 

 inessential they are : the more important and constant they are, 

 the more they are intermediate structures. For this reason, par- 

 ental characters in species-hybrids tend to be fused ; in variety- 

 hybrids to be more or less unmodified. Whether the one or the 

 other parental form is used as the pollen parent is of little or no 

 significance, so far as the characters of the hybrid are concerned. 

 Nageli holds, however, that the exchange of parents in reciprocal 

 crossing brings about a modification of inner characters in the 

 hybrid, which become evident in unlike fertility and in an unlike 

 tendency to vary in the progeny, {ib.) 



8. "The rule that the characters of the hybrid plant move between the 

 corresponding ones of the parental forms does not hold good in a strict 

 sense." {ib., p. 225.) 



Some characters, by virtue of individual variation, may extend 

 over this boundary, which happens the more, the more nearly re- 

 lated to each other the parental forms are ; hence, most nearly in 

 the case of little different varieties. The variation from the rule in 

 the case of species-hybrids assumes a general character, through 

 the fact that the hybrids of nearly related species become weakened 

 in the reproductive organs, but luxuriate in the vegetative organs, 

 and that the hybrids of more distantly related species develop 

 feebly in all their parts, and soon die out through lack of vital 

 energy, {ib.) 



9. "In general, hybrids vary so much the less in the first generation, 

 the farther the parental forms are removed from one another in re- 

 lationship ; thus species-hybrids less than variety-hybrids. The former 

 are often distinguished by great uniformity, the latter by great diversity." 

 {ib., p. 230.) 



If the hybrids are self-fertilized, the variability increases in the 

 second and succeeding generations by so much the more, the more 

 completely it was lacking in the first. The farther apart the paren- 

 tal forms lie, the more certainly the offspring in the second and suc- 

 ceeding generations fall into the three-. distinct varieties, one which 

 corresponds to the original type, and two others which are more 

 similar to the parental forms (Stammformen). These varieties 

 have, however, at least in the next generation, little constancy; 

 they change easily into one another. An actual reversion to one 

 of the two parent forms (on pure in-breeding) occurs especially 

 when the parental forms are very nearly related; thus with the 



