446 THE VASCULAR PLANTS 



F. Plant Breeding. Fertilization is the basis of plant 

 breeding. What is in sperm and egg limits the nature of 

 the individual which results from their fusion. 



Breeding means the effort by man, through control of 

 reproduction, to obtain a progeny better for his purposes 

 than its progenitors were. It is commonly described as 

 effort to improve the stock. 



Breeding can be understood only if certain fundamental 

 facts are understood and their application appreciated. 

 With some of these facts you are already familiar. One 

 of them is the fact of variation, the fact that no two indi- 

 viduals are precisely alike. Remember that nature pro- 

 duces multitudes of individuals, but that it was man, seek- 

 ing to interpret nature, who determined which groups of 

 these multitudes of individuals we shall call kinds or species. 

 Often it is impossible to tell ''where one species stops and 

 another begins" so complete are the inter grades between one 

 kind and another. This universal tendency to variation 

 makes it possible for man to select those forms preferred. 

 If the selected forms remain true to type, that is, if they pro- 

 duce individuals much like the selected parent forms, an 

 improvement has been made. 



But variation hinders as well as helps. The progeny 

 of selected forms may not remain true to type. They are 

 as likely to resemble their inferior grandparents as their 

 superior parents. For this reason thoroughbred forms are 

 more valuable than those forms which, though themselves 

 superior, have an unknown ancestry. Thoroughbred or 

 pedigreed stock is stock whose ancestry for several genera- 

 tions is known by records to have been of superior grade. 

 Now that plants are being scientifically bred as well as 

 animals, we are beginning to hear of "thoroughbred" corn 



