Plants in Relation to Man 513 



this experiment in combining the characters of the wild with 

 certain qualities of modern cultivated wheat will transform 

 sections of the country too dry for domestic wheat into wheat- 

 producing regions. Cross-pollination, moreover, always means 

 wide variation, and this makes possible more rapid improve- 

 ment in the varieties of a plant. 



248. Many unit characters in parent plants. In all efforts 

 to improve plants it must be recognized that in every parent 

 plant there may be many unit characters of different kinds. 

 This complicates the problem, but the same law applies as 

 well as when only two characters are involved. Each unit 

 character is somehow independent, never blended with others, 

 and may by proper control be isolated from them. 



Desirable characters. In cultivated plants such characters 

 as vigor in germination and growth, strength, health, resistance 

 to cold and drought, productiveness, together with a certain 

 size and quality of fruit, are generally desired. It may be that 

 not all these characters are combined in any individual plant 

 or variety. But by intelligently applying the principles of the 

 inheritance of unit characters, one may by selection and con- 

 trolled cross-pollination successfully combine them in a new 

 variety of great economic value. This involves testing, select- 

 ing, and controlled fertilization. It calls for patience at every 

 step. Selected plants must be accurately marked, and a com- 

 plete record kept, in which are given the characters and results 

 in each generation. Although the rejection of thousands of 

 good individuals may be necessary, if the final result is the 

 evolution of the desired variety, this will more than compensate 

 for the cost. 



SUMMARY 



A knowledge of the laws of heredity is important for all who are 

 interested in human welfare. 



To Gregor Mendel, an Austrian monk, is due much of the modern 

 scientific knowledge about heredity. 



Mendel discovered that unit characters, such as dwarfishness and 



2L 



