1908.] 



IMPROVEMENT OF THE POTATO. 



403 



changes. That mutative changes do take place, we are certain ; but 

 nothing is known of their character or frequency. I believe that po- 

 tatoes are very good material with which to throw some light upon 

 the subject. It is only just to note, however, that the experimental 

 work reported in this paper was planned and executed before Jo- 

 hannsen reported his experiments. The experiment has now been 

 revised to better fit the problem. 



EXPERIMENTAL EVIDENCE 



Believing that the practical experiments in tuber selection are 

 of some value, we have made a study of the reported results. 



As early as 1860 Hellriegel (55), from a three years' experi- 

 ment, came to the conclusion that it is not possible to improve a 

 variety of potatoes in starch content by the selection of tubers hav- 

 ing a high specific gravity. His experiments gave the following 

 starch contents from selections of tubers of high and low specific 

 gravity : 



It can be seen that the slight difference shown here might easily 

 be due to experimental error and that there is no cumulative effect 

 due to the selection. 



Franz (36) in 1878 concluded that from his experience and 

 from general farm practice that varieties at least could be kept up 

 in vigor by the selection of the seed. 



Emery (30) took a step in advance in method and used one 

 hundred tubers from poorest hills as compared with one hundred 

 tubers of the same weight from the best hills. His results were ir- 

 regular and he came to no conclusion. 



Wollny (no) took a further step toward lessening experimen- 

 tal error, and used only tubers of the same weight, but he concluded 

 that selection of tubers with a high specific gravity shows no defi- 

 nite influence upon the progeny either in quality or amount of yield. 



Later Marek (69) opposed these conclusions. His work is 

 weak, however, from the fact that he divided his tubers into dif- 

 ferent sizes, and after finding that the heaviest tubers were highest 

 in specific gravity, he used them as seed. The results were probably 

 due in great measure to the heavier seed piece used. 



