GENERAL BRACTS CONCERNING HEREDITY. l7 



improver of plants to continue a student and not a practical pro- 

 ducer of values. On the other hand, those who seek for values are 

 too much open to the accusation of not jjroperly reading, and of not 

 recording for others the way nature would have the breeder follow 

 in producing new forms. IJoth classes of men are needed; also those 

 who broadly combine the scientific and practical. 



Some of the important principles and facts to be observed in 

 improving plants may be enumerated as follows : 



(1) The individual plant produced from a seed is the imjiortant 

 unit in plant breeding. The "bud unit," though of much consequence 

 in case of marked bud variation, is usually of minor importance. 



(2) Heredity, centripetal-like, enables us to produce from certain 

 choice plants many descendants which, on the average, quite resem- 

 ble their parents. 



(3) Variation, centrifugal-like, causes the production among the 

 descendants, along with very many average plants, of a few very 

 good individuals and a few very poor ones. 



(4) Bj^ selecting those best plants which upon trial produce superior 

 progeny, the whole variety may be slightly or considerably imi^roved. 



(5) Since the plants of each succeeding generation also vary, by 

 reijeatedly choosing the best the variety or race is further improved. 



(0) In many cases crossing increases the average vigor of the 

 progeny, but in other cases it decreases^ the average vigor, size, or 

 other desirable characteristics. 



(7) In all cases crossing increases variation, as a rule, both toward 

 better plants and toward poorer ones, thus giving opportunity for 

 selecting from among the best jjlants individuals which are superior, 

 as pi'ogenitors of varieties, to any individuals which could have been 

 secui-ed without crossing. 



(8) New varieties can best be founded upon one to a dozen superior 

 selected or cross-bred seedling plants used as parents. 



(!•) Very large numbers of individuals must be used from which to 

 select- or bleed in order that mothei- plants may certainly be discovered 

 from whicli su^X'i-ior varieties will spring. 



(10) In addition to growing large nund)ers, the breeder of plants 

 should grow all the plants of a given stock under uniform conditions, 

 tliat they ma}'^ be accurately compared. 



(11) Tli(^ testing of the finished variety must include adaptability 

 to the soil and climatic conditions, the quality and value of the result- 

 ing croj), and the relative cheapness and practicability of its pro- 

 duction. 



THE USE OF VARIATION ILLUSTRATED, 



Variation occurs in each and every characteristic of every class of 

 living organisms. While nearly all of the individuals of a species, 

 variety, strain, i)i-eed, or family resemble the average of their class in 



2;J2iJ7~No. w'U— 01 -2 



