56 BREEDING 



tall and a dwarf will not be seen till the spring of 

 1911, the result of a cross made on the same day 

 between a plant which had yellow cotyledons and 

 one which had green, will be seen in the autumn of 

 the same year, namely 1910. 



Before we proceed to describe the reappearance 

 of the parental characters in the second hybrid 

 generation, let us pause to consider the Mendelian 

 phenomenon manifested by the colour of the coty- 

 ledons, and compare it with the other instances of 

 it with which we have dealt up to the present. 



So far as we know, yellowness is a simple dominant 

 to greenness, in the case of the cotyledons in Pisum, 

 just as tallness is to dwarf ness. That is to say, no 

 difference between the pure yellow and the hybrid 

 yellow has so far been detected ; but it does not 

 seem to me unlikely that a difference between them 

 may be revealed by spectral analysis. 



It is curious that yellow is dominant over green 

 in the case of the cotyledons, in view of the fact that 

 in the case of the pods green is dominant o^er yellow, 

 according to Mendel's account. 



We will now follow up the results of the supposed 

 cross that was made in the summer of 1910. As a 

 matter of fact, I did make many such crosses during 

 that summer. 



In our supposed cross a flower of a plant raised 

 from a green seed was pollinated in the summer of 

 1910 from a flower of a plant raised from a yellow 

 seed ; and in the autumn of the same year the result 



