132 Heredity and Eugenics 



of selection must be the average condition of the progeny 

 of a plant determined by actual field tests. The entire 

 object of selection is accomplished when a homozygous 

 strain or strain genotypical for the desired qualities is 

 isolated. The idea is simple; to put the idea into practice 

 successfully is often a tedious and difficult task. 



As in hybridization, the ease with which results can be 

 obtained by selection depends largely upon flower structure. 

 In selection, however, the relative facility with which 

 artificial cross-pollination can be accomplished is of small 

 importance. What one wishes to know is whether cross- 

 pollination or self-pollination takes place naturally. 



Practically all plants are occasionally cross-fertilized 

 naturally, and many of them have devices whereby they 

 are nearly always crossed; but, as we have already seen, 

 though cross-fertilization is an advantage to a plant, it is 

 not at all essential. Wheat, for example, is almost always 

 self -fertilized; yet it has kept its vigor for thousands of 

 years. The importance of this fact to the selectionist is 

 readily seen. If seed from several varieties of wheat is 

 mixed and planted, each variety remains true to its type 

 because of self-pollination, and each strain can be recovered 

 in one generation. In like manner, if desirable variations 

 occur in a wheat variety, it is a simple process to sepa- 

 rate them from the parent strain for the two are mixed 

 mechanically. It is only necessary to save seed from 

 individual plants and grow them in separate rows or plots. 

 One can see immediately whether the desirable variation 

 is inherited or not, and if so the thing is done. 



In a cross-pollinated plant the method is the same, but 

 the work is not so easy. The pollen is carried through long 

 distances by the wind or by insects, and even with carefully 



