CHAPTER XIX 



PLANT BREEDING 



176. Definition. The purpose of plant-breeding is to 

 improve cultivated plants, just as the purpose of animal- 

 breeding is to improve domesticated animals. Great pro- 

 gress has been made in the science of plant-breeding, so 

 that it is possible now in many cases to breed for certain 

 desired improvements with great confidence that they will 

 be secured. The skilful plant-breeder not only must know 

 how to make plants grow, but he must know also the laws 

 connected with the reproduction of plants. 



177. Variation. The fact with which the plant-breeder 

 starts is that plants tend to vary. If all the seeds from one 

 parent plant are sown, the plants that come from them 

 will all resemble the parent in a general way; this handing 

 down of similarities from one generation to the next is called 

 heredity. But while there is this general resemblance to the 

 parent, there are variations, one or more of the new plants 

 perhaps resembling the parent less than the others do. It 

 is this fact that makes plant-breeding possible; and instead 

 of relying upon nature to present to him all the variations 

 he needs, the plant-breeder by changing conditions increases 

 the tendency of plants to vary, and also by crossing multi- 

 plies variations. The important thing is to obtain as many 

 and as wide variations as possible. 



178. Vegetative propagation. If among varying plants 

 there appears one that is desirable, it may be possible to 

 propagate it vegetatively, that is, without using the seed. 



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