3o6 PLANT-BREEDING 



figures for some 40,000 beets, cultivated on the fields of 

 Messrs. Kuhn & Co., at Naarden, in Holland, and examined 

 in their laboratory for purposes of selection. The average 

 percentage was 15.5, the extremes going up to 19 and coming 

 dov^n to about 12 per cent. These extremes, however, 

 were comparatively very rare, especially on the upper side 

 of the group, where only a few individuals reached the very 

 Hmit. More than one half of all the beets differed less than 

 one-half per cent from the average, the total number of 

 roots with 15 to 16 percent sugar being about twenty-two 

 thousand. On both sides of this central group the number 

 of beets rapidly decreased with the increasing degree of 

 deviation from the average value. 



In the same manner the fluctuating variability of other 

 quahties and other characters may be given under the form 

 of a curve. The ray-florets on the heads of the composites 

 can easily be counted for hundreds and even for thousands 

 of single flower-heads, and the figures thus obtained will 

 show a similar grouping around an average number. In the 

 marigolds this number is 13, in the daisies 21, and the same 

 figures are met with on the flower-heads of numerous other 

 species. The size of fruits and capsules may be treated 

 in the same way. I measured the capsules of over five 

 hundred incUviduals of an evening primrose and got a curve 

 that did not differ essentially from that of the sugar beets 

 just mentioned. The average individuals bore capsules of 

 nearly 2.5 cm. and the extremes reached 1.5 and 3.4 cm. 

 The largest capsules were thus seen to have about double 

 the size of the smallest ones. Between these limits the 

 different sizes were grouped in such a way that more than 

 half of the individuals could be said to have fruits of medium 

 size, the remaining sizes being respectively rarer the more 

 they differed from the average. 



If now we compare this size of the capsules of the evening 



