4 2 



ZOOLOGY 



Mendel's 

 guiding 

 principle in 

 crossing 

 plants 



Fortunately his work with plants, which led him to the 

 remarkable generalizations now everywhere associated 

 with his name, was described at some length in papers 

 communicated to the natural history society of Briinn. 

 Mendel's originality and sagacity were shown at the 

 very beginning of his work, in his selection of plants 

 with which to work. The problems which interested him 

 were those of inheritance, and he saw that it was neces- 

 sary to find plants which possessed constant and easily 

 recognizable differentiating characters, but which would, 

 nevertheless, cross without any marked impairment of 

 fertility in successive generations. It was also desirable 

 to find a species which could be easily grown, and would 

 not be too liable to cross-fertilization by insects, which 

 would of course spoil the statistical results. The great- 

 est discoveries in science have usually been made with 

 the most commonplace materials, and in this case 

 Mendel chose for his principal investigations the or- 

 dinary cultivated pea, in its several common varieties. 



2. Mendel worked for eight years with his peas, and 

 when he came to publish his results, he stated his guid- 

 ing principle as follows : 



'Those who survey the work done in this department 

 (of hybridization) 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 possible to determine the number of different 

 forms under which the offspring of hybrids appear, or 

 to arrange these forms with certainty according to their 

 separate generations, or definitely to ascertain their 

 statistical relations. It requires some courage to under- 

 take a labor of such far-reaching extent ; this appears, 

 however, to be the only right way in which we can 

 finally reach the solution of a question, the importance 



