Princij)les of Heredity 187 



plants afford an admirable illustration of the effect produced 

 by crossing a few pairs of plants of known ancestry ; but while 

 they show this perhaps better than any similar experiment, 

 they do not afford the data necessary for a statement as to the 

 behaviour of yellow-seeded peas in general, whatever their 

 ancestry, when crossed with green-seeded peas of any ancestry. 

 [Mendel of course makes no such statement.] 



" When this is remembered, the importance of the exceptions 

 to dominance of yellow cotyledon-colour, or of smooth and 

 rounded shape of seeds, observed by Tschermak, is much in- 

 creased ; because although they form a small percentage of his 

 whole result, they form a very large percentage of the results 

 obtained with peas of certain races. [Certainly.] The fact that 

 Telephone behaved in crossing on the whole like a green-seeded 

 race of exceptional dominance shows that something other than 

 the mere character of the parental generation operated in this case. 

 Thus in eight out of 27 seeds from the yellow Pois cFAuvergne 

 $ x Telephone the cotyledons were yellow with green patches ; 

 the reciprocal cross gave two green and one yellow-and-green 

 seed out of the whole ten obtained ; and the cross Telephone 9 

 x (yellow-seeded) Buchsbaum* gave on one occasion two green 

 and four yellow seeds. 



"So the cross Couturier (orange yellow) <J? x the green -seeded 

 Express <$ gave a number of seeds intermediate in colour. (It 

 is not clear from Tschermak's paper whether all the seeds were 

 of this colour, but certainly some of them were.) The green 

 Plein le Panier \_Fillbasket\ $ x Couturier <$ in three crosses 

 always gave either seeds of colour intermediate between green 

 and yellow, or some yellow and some green seeds in the same 

 pod. The cross reciprocal to this was not made ; but Express 9 

 x Couturier gave 22 seeds of which four were yellowish 

 green t. 



"These facts show first that Mendel's law of dominance 

 conspicuously fails for crosses between certain races, while it 



* Regarding this " exception " see p. 146. 

 t See p. 14ft. 



