34 APPLICATION OF PRINCIPLES OF HEREDITY TO BREEDING. 



separate. It may happen that some of the selections thus made 

 are superior because they have been grown under very favorable 

 environment and that another year when the environment is less 

 favorable they may prove to be very inferior. Others may prove 

 to be superior under a wider range of environmental conditions, so 

 that from year to year they will be superior. The next year mass 

 selection would be mostly from those plants wiiich are what we may 

 call permanently superior, together with a few of those which merely 

 happen to be superior under the given conditions. The contin- 

 uation of mass selection thus tends to improve from year to year 

 the general character of the crop, but it does this by the gradual 

 elimination of the progeny of those plants which are not superior 

 except under very favorable conditions. This gradual improve- 

 ment that occurs in mass selection has misled biologists and plant 

 breeders generally into believing that selection could affect fluctu- 

 ating variation. 



The effect of mass selection of self -fertilized crops is well illustrated 

 by some of Prof. C. A. Zavitz's work at Guelph, Ontario, Canada. 

 In his annual report for 1905 he gives the results of sixteen years' 

 continuous mass selection on oats and barley. These are given 

 below. For convenience, his results obtained by similar methods 

 with potatoes are also given here. It will be noticed that mass 

 selection has the same effect in seh-fertilized wheat and oats as in 

 potatoes, which are propagated vegetatively. 



Table III. — Average yields hy four-year periods, in bushels per acre, of oats, barley, 

 and potatoes, showing the effect of mass selection on self fertilized and on vegetatively 

 propagated crops. 



Crops. 



1890-1893. 



1894-1897. 



1898-1901. 



1902-1905. 



Oats, average for 8 varieties 



Barley, average for 8 varieties 



Bushels. 

 74 

 50 

 120 



Bushels. 

 79 

 54 

 216 



Bushels. 

 83 

 63 

 218 



Bushels. 



100 

 63 

 249 



The very marked effect in the case of potatoes is probably due to 

 degeneration which had occurred in many vegetative strains before 

 the selection began, the progeny of these degenerate strains being 

 gradually eliminated by mass selection. 



The Mandscheuri barley, now so largely grown in Ontario, is 

 descended from a single pound of seed obtained from Prussia in 

 1889. Of this variety 567,000 acres were grown in Ontario in 1908. 

 Since the introduction of Mandscheuri, the barley crop of Ontario 

 has increased in value from $4,800,000 to $12,900,000, and this is in 

 part due to the larger yielding power of this variety. The greater 

 profit due to larger yields has caused an increase in acreage. 



165 



