308 Retrograde Varieties 



do so in nearly all tlie crosses made for prac- 

 tical purposes, and in very many scientific ex- 

 periments. Even Mendel's peas were not pure 

 in this respect, much less do the campions noted 

 above differ only in Mendelian characters. 



Comparative and systematic studies must be 

 made to ascertain the true nature of every unit 

 in every single plant, and crossing experiments 

 must be based on these distinctions in order to 

 decide what laws are applicable in any case. 



