220 



Science of Plant Life 



Plant breeding. Reproduction in plants is the 

 foundation upon which the important industry of plant 

 breeding is being built. Plant breeding is concerned 

 with the improvement of economic plants and with 

 the production of new plants of economic value. The 

 activities of plant breeders are 

 being directed toward four 

 principal objectives : (i) the 

 breeding of plants with more 

 desirable products, as flowers, 

 fruits, leaves, and fibers ; (2) the 

 breeding of new varieties which 

 will increase the yield per acre ; 

 (3) the securing of varieties 

 better fitted to particular cli- 

 mates and soils ; and (4) the 

 producing of varieties capable of 

 greater resistance to diseases. 



Plant breeding with these pur- 

 poses is possible and profitable 

 because (i) variations naturally 

 occur among plants ; (2) some 

 variations are inherited and 

 may be preserved by selection; 

 and (3) different varieties and 

 species may be crossed to pro- 

 duce hybrids having a still larger 

 range of variations than the 



number of seeds produced, and by parent plants Or possessing new 



selecting seed from only the plants com binations of desirable quali- 



with long spikes the yield of seed may 



be increased several fold. tlCS. 



FIG. 136. Timothy spikes. The heads 

 show great variation in length and 



