3o8 PLANT-BREEDING 



of the roots and of the foliage. One of these two main 

 points, of course, is the percentage of sugar in the sap. The 

 other point is the quahty of the seeds, since on this quality 

 the harvest of the next year chiefly depends. Now it is 

 evident that of our two groups of causes which determine 

 the phenomena of correlation of fluctuating variability, only 

 the second one comes into consideration. This correlation 

 may be simply stated by saying that, as a rule, stouter plants 

 will be richer in sugar and produce better seeds. Nearly 

 all other causes, however, which govern the amount of sugar 

 in the roots of the first year will be without influence on the 

 quality of the seeds. Local variations in soil, in moisture, 

 and especially in the amount of space, when this is increased 

 on account of the falUng out of some neighbor, will directly 

 influence the sugar percentage, which may also be dimin- 

 ished by insects feeding on the leaves or by other diseases. 

 In the second year the roots will be planted in other fields 

 and with other conditions of soil and exposure, and during 

 the time of production of seeds the single individuals will 

 occupy quite different places on the curve of variability than 

 those they held the first year. 



Hence we may conclude that the correlation between the 

 percentage figure for the root of the first year, and the real 

 value of the seeds is only a very feeble relation. The richest 

 roots may yield only poor seeds and conversely. In other 

 words, the percentage figures, which are now the universally 

 accepted criterion for the selection of beets for the produc- 

 tion of seed, are only an imperfect indication of the quality 

 of the latter. Direct experiments have often shown the 

 accuracy of this conclusion, and the breeders of sugar-beets 

 know very well that single excellent roots may not be relied 

 upon at all for the production of exceptionally good seed. 

 They rely only on the average of the selected beets, and 

 rightly assume that the larger the group of their roots, the 



