GERMINAL ANALYSIS THROUGH HYBRIDIZATION. 



By GEORGE HARRISON SHULL. 



(Read April 23, igio.) 



The study of the various characteristics of plants and animals 

 as independent units has made hybridization a valuable instrument 

 in experimental morphology, and has given to the name of Mendel 

 an enduring place as a true prophet in the history of biological 

 progress. 



The importance of the Mendelian contribution can scarcely be 

 over-estimated. Before the " re-discovery " a decade ago, no one 

 but Mendel had given an approximately correct interpretation of 

 the composition and behavior of hybrid progenies, and the process 

 of hybridization was therefore of no particular consequence for 

 general biology. The hybrid individual was taken as the unit and 

 comparisons between the hybrids and their parents were made in 

 generalized terms involving the general aspect or tout ensemble. 

 As only rarely were all the characteristics of either parent recom- 

 bined in one of the offspring, the phenomena of segregation and 

 recombination were considered of relatively rare occurrence, and 

 described in terms of atavism or " throwing back " to the ancestral 

 condition. 



An important cause for the long delay in the discovery of the 

 Mendelian phenomena was the distinction made between the off- 

 spring of species-crosses, which alone were distinguished as 

 " hybrids," and the cross-bred offspring of more closely related forms, 

 which were stigmatized as " mongrels." The difficulty of making 

 species-crosses, the consequent rarity of such hybrids, and the 

 usually uniform type of the offspring produced, all gave the im- 

 pression of their greater scientific importance at a time when 

 rarity and uniformity of phenomena instead of their general occur- 

 rence and variability seem to have made the stronger appeal. 



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