382 EXPERIMENTAL STUDY OF INHERITANCE 



in other cases the unit-characters are not so " exclubive," but 

 may combine with analogous unit characters to form a blend or 

 a particulate mosaic. 



Non-Mendelian Results. — In a lecture on Heredity which the 

 late Professor Wei don delivered in 1905, an account was given 

 of some of Tschermak's experiments on peas and beans, the results 

 of which do not harmonise well with the Mendelian formula. 

 (See The Lancet, March 25, 1905, p. 810.) 



Tschermak crossed two races of peas characterised by cotyledons 

 of two different types of growth, — epigeal and hypogeal. The 

 hybrid progeny of the crossing showed 30 plants with epigeal 

 cotyledons, 32 with the hypogeal habit, and 18 of intermediate 

 type — obviously " a very imperfect segregation." In the third 

 generation none of these bred true ; each produced, when 

 fertilised by its own kind, a mixed progeny of all the three sorts. 



Tschermak crossed a white-flowered pea {Pisum sativum) with 

 a red or purple species (Pisum arvense) ; the hybrid progeny 

 resembled the latter ; the red colour was dominant. But 

 when these were fertilised from their kind, they yielded out of 

 397 plants, 239 red, 75 rose, and 83 white — a proportion of 9 red, 

 3 rose, and 4 white, which cannot be called Mendelian. Tschermak 

 suggested, however, that if white and rose were postulated as 

 the ancestral colours of the two races of peas, the results would 

 more closely conform to the Mendelian formula. 



Tschermak went on to work with the red (239), rose (75) and 

 white (83) plants, fertilising each type from its own kind, and he 

 found that of the reds some produced red and others white and 

 rose-coloured offspring, that of the whites the offspring were 

 mostly white, while most of the rose-coloured plants yielded 

 only a rose-and- white progeny. This, again, does not seem to be 

 a Mendelian result. 



Tschermak also crossed bronze and white kidney beans, and 

 got a hybrid progeny with seed-coats of a dark brown colour 

 mottled with black spots and " tortoisesheU " markings (488 



