Plant-Breeding for Farmers. 135 



ful gardeners learn to recognize the individual plants which they handle 

 day after day the same as the shepherd recognizes the different members 

 of his flock. These ordinarily slight variations which are spoken of 

 commonly as individual variations are what the scientists now call con- 

 tinuous or fluctuating variations. 



All of the individuals of any species, rase or variety, whether wild or 

 cultivated, show these individual variations. If we examine the different 

 seedling trees in nursery rows of maple or oak, or different corn or wheat 

 plants in fields of the same race, we will find them to present similar 

 individual variations. These variations are congenital, that is are born 

 with the individual, and are apparently not caused as a direct result of 

 of the environment. In many cases such variations are transmitted by a 

 plant to its progeny in the same manner that many of the individual 

 characters or characteristics of a human being are in part at least trans- 

 mitted to his progeny. 



Such slight individual variations are the type of variation most used 

 by animal-breeders in selecting to improve the breed. In plant-breed- 

 ing such individual variations are also used when the breeder is selecting 

 to produce an improved strain of any race. If, for example, the breeder 

 desires to produce a heavy yielding strain of the Pride-of-the-Xorth corn, 

 he would select individuals having the maximum yield, plant these in 

 isolated places and continue the selection year after year, until a high 

 yielding strain of the variety had been produced. In such a selection the 

 scientist would assume that there had been no change produced in the 

 type of the race but that the breeder by the selection and isolation of the 

 maximum yielding individuals had produced a family, within the race, of 

 high yielding capacity, this being maintained continually by the selec- 

 tion. If, however, the selection and isolation of the highest yielding 

 plants was discontinued and free intercrossing with inferior individuals 

 was allowed, the mean yielding capacity of the race as a whole would 

 soon be established again. 



A second type of variation is that known to gardeners and horti- 

 culturists as sports and to the scientists as mutations. These are large 

 pattern, striking variations which do not occur very commonly, but 

 which, when found, are likely to prove useful in the production of new 

 types of value. The recent scientific studies of De \^ries. a famous 

 botanist of Holland, have emphasized the great importance of such 

 variations in the production of cultivated varieties and the evolution of 

 species. As is well known to gardeners these sports or mutations, appear 

 suddenly without warning or reason so far as we know. We cannot pro- 

 duce them and must simply wait until they appear and then be prepared 

 to recognize and propagate them. Mutations usually reproduce their 

 characters without much reversion to the parental type except such as is 



