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 
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