230 BREEDING CROP PLANTS 



For the 16-year period from 1890 to 1905, inclusive, the 

 varieties were kept in a high state of productivity "due, no 

 doubt, to careful selection and good cultivation each year. " In 

 1906, however, there was a marked falling off in yield due to the 

 unfavorable season. In the early part of the season there was 

 sufficient rain but at about the time of the last cultivation, hot 

 dry weather set in and continued throughout the season. During 

 July there was also a severe attack by aphis. The vines, therefore, 

 presented a stunted appearance and dried up early in the fall, 

 the yield of tubers being very low. In 1907 and 1908 the seasons 

 were also very unfavorable. The best tubers were again planted 

 in 1909 and although the tubers used for planting presented a 

 very favorable appearance, the yields were very low. A com- 

 parison was made in 1909 of tubers grown continuously at the 

 Central Experiment Farm and newly imported tubers grown under 

 more favorable conditions. The yielding ability of the imported 

 tubers exceeded that of the Central Farm tubers by as high as 

 500 per cent, in some cases. 



The plant breeder is naturally interested in the subject of 

 whether these are instances of bud variations due to unfavorable 

 environment. If so, they should be permanent changes. If, 

 on the other hand, they are non-heritable variations, this does 

 not affect the practical importance of tuber selection as a means 

 of obtaining high yields. Macoun (1918) has furnished evidence 

 which helps to clarify our ideas on this question. From time to 

 time tubers were sent from Ottawa to the branch stations, on the 

 prairies, where potatoes usually grow very vigorously. In 1916 

 the following question was asked: 



"You will, no doubt, remember that potatoes sent you from Ottawa 

 are usually weak growers when you receive them. I would be glad if 

 you would inform me for how many seasons that weak growth con- 

 tinues, or do they make a strong growth the next year, the same as 

 the ones you have been growing for several years?" 



Answers made by the superintendents of these prairie farms 

 showed that the first year's crop from tubers sent from the Cen- 

 tral Farm was very small. From one to three years elapsed 

 before varieties introduced from the Central Experimental 

 Farm yielded as well on the prairies as those varieties which had 

 been continually grown on the prairies. 



Much of the so-called "running out" or degeneracy in pota- 



