24 MENDELISM CHAP. 



occur, can be readily calculated. Moreover, as 

 Mendel showed, we can calculate also the chances 

 of any given form breeding true. To this point, 

 however, we shall return later. 



Of Mendel's experiments with beans it is sufficient 

 to say here that they corroborated his more ample 

 work with peas. He is also known to have made 

 experiments with many other plants, and a few of 

 his results are incidentally given in his series of letters 

 to Nageli the botanist. To the breeding and cross- 

 ing of bees he also devoted much time and attention, 

 but unhappily the record of these experiments 

 appears to have been lost. The only other published 

 work that we possess dealing with heredity is a brief 

 paper on some crossing experiments with the Hawk- 

 weeds (Hieradum\ a genus that he chose for working 

 with because of the enormous number of forms under 

 which it naturally exists. By crossing together the 

 more distinct varieties, he evidently hoped to pro- 

 duce some of these numerous wild forms, and so 

 throw light upon their origin and nature. In this 

 hope he was disappointed. Owing in part to the 

 great technical difficulties attending the cross-fer- 

 tilisation of these flowers he succeeded in obtaining 

 very few hybrids. Moreover, the behaviour of those 

 which he did obtain was quite contrary to what he 

 had found in the peas. Instead of giving a variety 

 of forms in the F 2 generation, they bred true and 

 continued to do so as long as they were kept under 

 observation. More recent research has shown that 

 this is due to a peculiar form of parthenogenesis 

 (cf. p. 123), and not to any failure of the characters 

 to separate clearly from one another in the gametes. 



