VARIATION AND HEREDITY 



period of very active experiment, in connec- 

 tion with which Bateson, Castle, Cuenot and 

 their collaborateurs have been especially 

 prominent. 



MmiHgl wnrlrpr] ptii'pfly with the qdible pea. 

 Pisum sativum, which has many well-marked 

 varieties and is habitually self -fertilized. 

 When he crossed a giant variety of 6 to 

 7 feet with a dwarf variety, f to ij feet 

 high, the offspring were all tall. The charge- 

 t^er of tajjlness which appeared in the hybrid 

 generation (F 1 ), to the exclusion of dwarf ness, 

 was called by Mendel tlje "dominant" 



The tall cross-bred peas were left to self- 

 fertilize, which corresponds to close inbreed- 

 ing in animals, and in their progeny there 

 were tails and dwarfs in the average pro- 

 portions of 3: 1. 



When the dwarfs of this F ?t generator*" 

 allowed to self-ffirti1J7ft r t-hfir 



nil rliy^fgij and further generations bred 

 from them were also all dwarfs. They may 

 be called pure recessives^ being "pure" a$ 

 regards dwarf ness. 



But wheji the tails of the T? g 



left to self -fertilize, tlimr nffgp^Tipy (T? g ) were af 

 two k^nds: one-thir^ of them (pnrp 



them (impnrp (](>nninfl.nt.s) produced tails 



