No. 7. DEPARTMENT OF AGRICULTURE. 483 



way to improve their varieties — of growing the plants which were 

 to be used as seed stocks in very rich, deeply worked soil where they 

 were very much crowded together; so much so that 16 to 20, or even 

 more, grew on one square meter of ground. The result was that 

 the beet assumed the form and later the length of a Avhipstock. 

 They were not branched because the roots were very closely crowded 

 together. Their sugar content was abnormally high as a result of 

 their growing so close together, and the conclusions drawn from the 

 form of the roots and their sugar content, as determined in the 

 laboratory, were tainted with error because they did not represent 

 qualities truly acquired, but modifications accidentally imposed by 

 external conditions. Thus these beets which were declared to be 

 of good shape and composition in the laboratory, yielded seed which 

 when sown in the open field, produced branched roots of only mod- 

 erate sugar content, because the descendants had reassumed their 

 true characters when they were released from the restraint which 

 had been artificially imposed uron the parent plants." 



Crossing: Crossing two unlike forms or two varieties may not be 

 a fundamental cause of variation. Some other cause must have 

 operated to produce the two unlike forms. In practice, however, 

 crossing is a means of inducing variation, so as to enable the breeder 

 to select form more nearly suited to his ideal. This is shown by 

 Hays in the case of a hybrid between Fife and Blue Stem wheat. 

 He found that some of the plants of hybrid wheat yielded more and 

 Fome less than any of the plants of either the Fife or of the Blue 

 Stem. If the yield is the characteristic desired, then a few plants 

 of the hybrid were better than either of the present varieties. 



Grossing is also employed not only to induce variation, but to com- 

 bine two or more desirable qualities in one plant. 



Selection: Plants having varied either through the efforts of the 

 breeder or otherwise, the next step is to select plants having the 

 characteristics desired. "Selection is the surest and most powerful 

 instrument," Vilmorin declares, "that man possesses for the modi- 

 fication of living organisms." 



The unit of selection is the individual. In the case of wheat the 

 unit is not the seed, nor even the head of wheat, but it is the stool 

 containing several heads and many seeds which have been produced 

 from a single seed. In the case of the potato it is the single hill 

 and not the single potato. 



Only useful characters should be selected, because two characters 

 are more difficult to develop than one; three more difficult than two, 

 and so on. Some characters are mutually antagonistic, as extreme 

 earliness and either great size, or productiveness. To select wisely 

 requires deep study and good judgment. Varieties frequently deter- 

 iorate on account of unwise selection. This is especially true of 

 maize, although it is the field cron which it is the easiest to select. 



Testing Hereditary I'orms of Plants: Having selected a desired 

 form, it is next necessary to test its ability to transmit its char- 

 acters. Even though the sire Cplant furnishincr the pollen) may be 

 known, there is no certainty that the plant will transmit the char- 

 acters which it possesses. Different kernels from the same head 

 of wheat are known to yield unequally. Some variations are easily 

 fixed; others require generations of selection before the characters 



