290 PLANT HYBRIDIZATION BEFORE MENDEL 



only references to Mendel's paper in scientific literature before 

 1900, as already remarked, are the statements referred to above 

 in Focke and Hoffmann. 



Mendel was led to undertake his investigations through a 

 realization that some law must underlie the fact of the regular 

 reappearance of the same types of hybrids zuhenever the same 

 two species are crossed. 



He says : 



"The striking regularity with which the same hybrid forms always re- 

 appeared whenever fertilization took place between the same species in- 

 duced further experiments to be undertaken, the object of which was to 

 follow up the development of the hybrids in their progeny." (5d, p. 335.) 



". . . That so far no generally applicable law governing the formation 

 and development of hybrids has been successfully formulated can hardly 

 be wondered at by anyone who is acquainted with the extent of the 

 task, and can appreciate the difficulties with which experiments of this 

 class have to contend. A final decision can only be arrived at when we 

 shall have before us the results of detailed experiments made on plants 

 belonging to the most diverse orders." {ib., pp. 335-6.) 



The kernel of Mendel's method, and the revelation of his scien- 

 tific insight, which so far outstripped that of all previous inves- 

 tigators in the field of hybridization, appears in the following 

 paragraph : 



"Those who survey the work done in this department will arrive at the 

 conviction that, among all the numerous experiments made, not one has 

 been carried out to such an extent and in such a way as to make it pos- 

 sible to determine the number of different forms under which the off- 

 spring of hybrids appear, or to arrange these forms with certainty ac- 

 cording to their separate generations, or definitely to ascertain their 

 statistical relations." {ib., p. 336.) 



As Bateson says : 



"It is to the clear conception of these three primary necessities that the 

 whole success of Mendel's work is due. So far as I know this conception 

 was absolutely new in his day." {ib., p. 336, note.) 



In the first place Mendel devoted great care to the selection 

 of a plant for his experiments, the requisites being, as he says, 

 the possession of constant differentiating characters, freedom 

 from accidental crossing by foreign pollen, and fertility of the 

 hybrids. No one before Mendel had apparently grasped the neces- 

 sity for the employment of the following method as outlined by 

 him: 



