318 A TEXT-BOOK OF BOTANY 



Among them there may be found one or more with a desired 

 variation, or at least the beginnings of it. These plants are 

 preserved and the others destroyed. Often many thousands 

 of young plants are thus started, and most of them de- 

 stroyed. 



180. Selection. When a desired variation has appeared, 

 the work of improving and establishing it must follow. 

 This is done by means of selection, and it involves great care 

 and patience. The selected plants are carefully guarded, no 

 foreign pollen being allowed access to their flowers. Their 

 seeds are planted, and among the new plants that come up 

 those showing the desired variation are preserved and the 

 others are destroyed. This selection goes on generation 

 after generation until only the desired variety is produced. 

 It is then said to be established, and can usually be de- 

 pended upon to produce its kind. 



Even after a variety has thus been established, great 

 care must be used in selecting from the best plants seeds 

 for planting, or the variety will "run down/' It is a great 

 mistake to suppose that seeds from inferior plants will do just 

 as well for sowing as seeds from the best plants. Farmers 

 have learned this in selecting their seed-corn, seed-wheat, 

 etc. ; and their success depends upon their wise selection of 

 the seeds to plant. It is important to know that in this 

 selection of seed the character of the individual plant that 

 produces it is the important thing. To select for planting 

 the largest ears of corn from a pile of corn does not result so 

 well as to select in the field the plants that produce on the 

 average the best ears. 



The process of selection is being applied also in the 

 development of varieties that resist certain diseases. For 

 example, in a field that has been ravaged by some disease 

 a few plants may be found that have resisted the attack 

 successfully. This means that the variation in these plants 

 is a very desirable disease-resisting power. Starting with 



