4 GENETICS IN RELATION TO AGRICULTURE 



development are treated as separate sub-divisions of biology, such as 

 embryology, cytology, experimental morphology, and like subjects. 

 While obviously there is much in all of these subjects which is irrele- 

 vant to a treatment of genetics, nevertheless, rightly interpreted, there 

 is little which is essential to any one of them which does not bear some 

 more or less intimate relations to those phenomena which belong more 

 strictly in the province of genetics. The reason for this is very apparent, 

 the development of the individual is a consequence of the elaboration 

 of the hereditary material, it is the fulfillment of the possibilities wrapped 

 up in the germ cell; how then can it fail to possess much that is of very 

 great significance to genetics? Assuredly the further advancement of 

 the science of genetics will focus more and more attention upon the prob- 

 lems of growth and differentiation in the individual; for that reason these 

 emphatic statements are made. 



The Problems of Genetics. Obviously the problems of genetics 

 are those which grow out of a study of resemblances and differences in 

 individuals related by descent. Wilson has reduced the statement of 

 the problems of inheritance and development to that oft-quoted question : 

 "How do the adult characteristics lie latent in the egg; and how do 

 they become patent as development proceeds?" Pearl has voiced very 

 much the same thought in his statement that the critical problem of 

 inheritance is the problem of the cause; the material basis; and the 

 maintenance of the somatogenic specificity of germinal substance. 



There are four general methods of attacking the problems of heredity; 

 namely, the methods of observation, experimental breeding, cytology, 

 and experimental morphology. Each of these methods has its specific 

 advantage and particular value as well as its definite limitations. In the 

 following discussion each method is considered briefly with respect to its 

 relation to the development of the science of genetics. 



The Method of Observation. The method of observation, or de- 

 scription as it is often called, requires special treatment because it employs 

 the inductive mode of reasoning. Briefly the essential steps involved 

 in the application of inductive reasoning to the problems of genetics 

 may be stated as follows. The first step is the observation of the re- 

 semblances and differences between representative individuals of a 

 given line of descent or, if problems of evolution are under consideration, 

 of different lines of descent. The next step is a comparison of the ob- 

 servations which have been made for the purpose of determining whether 

 they show orderliness with respect to each other; in other words to de- 

 termine whether they probably have a common causal basis. If they 

 do show such orderliness, an attempt is made to formulate the principles 

 or laws which govern them. Finally, the principles or laws thus for- 

 mulated are applied to other instances not included in the original set of 



