SYSTEMATIC IMPROVEMENT OF PLANTS 199 



of inherently superior powers. This experiment is so easily 

 repeated that it is recommended for the student, and further 

 data are hardly necessary in the text (see table, p. 204). 



This method is akin to that employed for the increase of sugar 

 in the sugar beet. When the Germans commenced the improve- 

 ment of this crop, the sugar content was low, running from 4 to 

 6 per cent, while now whole fields run 1 5 per cent and occasional 

 single beets are found as high as 25 per cent. This improve- 

 ment has been effected in the following way. 



Many promising beets are analyzed for sugar content and 

 only the highest are selected for planting. The same process 

 is repeated for two or three generations, the best individuals 

 always being selected as " mother beets." The seed from the 

 last selection is " multiplied " in the open field by planting with- 

 out selection, simply to secure commercial quantities. Thus 

 the commercial seed, while not immediately descended from 

 selected beets, is but one or two generations removed from a 

 highly selected parentage. 



Crossing to produce new varieties. By the methods above 

 mentioned any strain or variety may be greatly improved, but 

 by the method of crossing we may bring together absolutely new 

 combinations of characters and thereby produce new varieties, 

 some of which are certain to be more useful than the old. 



The reasons which practically rule out crossing as a means 

 of improvement in animals, except in rarest cases, do not apply 

 with much force to plants, because we can produce them in such 

 enormous numbers and they are relatively so cheap that we can 

 afford to throw away the most of them for the sake of getting 

 the few or even the one that is useful. 



Application of MendePs law in crossing. The confusing ele- 

 ment in crossing is the behavior of dominant and recessive 

 characters when suddenly brought together in new combinations. 

 Reference to the chapter on Mendel's law will refresh the point 

 that characters combine in definite proportions, but that some 

 are much more apparent than others which are easily obscured, 



