36.; 



Pedigree culture or line breeding on a large scale is a main 

 method. In pure lines there are no hereditary variations, and 

 "no correlations between botanical characters and industrial 

 qualities." Value of pure lines determined only by the yielding 

 tests. This sort of line breeding isolates superior bio types. 



Artificial hybridization. — An important method in scientific 

 breeding. Importance at Svalof considered as based on the Men- 

 delian conception of alternative inheritance and the recombina- 

 tion of unit characters. It is followed by careful line breeding 

 of hybrid progeny. 



Variability 



No progressive mutations in cereals have appeared at the 

 Svalof station. 



Variations in cereals are largely due to natural hybridization. 

 Aberrant forms In grains are often cases of segregation in the 

 progeny of heterozygotes. 



Acclimatization is due to regrouping of factors in a hetero- 

 zygous population. The stronger combinations survive. 



Hereditary variations may be continuous where different 

 combinations ^ of different units are such that gradations in a 

 given character result. Continuous hereditary variations are 

 possible but are considered as based on the chance combination 

 of independent units (or fractions of a unit) which ultimately 

 form a multiple factor. 



In regard to the practical and theoretical study of variations, 

 the work with potatoes at Svalof is proving of special significance 

 as the potato is propagated vegetatively in what is essentially a 

 pure line. In the five years that potato breeding has been in 

 progress "continuous selection of desirable hills and tubers" 

 has resulted in improvement. 



In criticism it may be noted that this sort of continuous 

 hereditary variation is not to be explained on the basis mentioned 

 above and suggests that a Mendelian conception of continuous 

 hereditary variations is of doubtful validity. In fact much of the 

 data presented concerning variation not only in the vegetative 

 reproduction of potatoes but in the sexually reproduced cereals 



