10 GENETICS IN RELATION TO AGRICULTURE 



The Method of Experimental Morphology. Under the heading 

 morphology, we include those particular phases of development which 

 are designated by the terms, ontogeny and embryology. The method 

 of experimental morphology has for its task the solution of the problem 

 of the development of the individual as it is related to problems of 

 variation and heredity. The aim of this method is to determine how 

 the characters of the adult become patent as development proceeds, the 

 broad question of the origin of complexities within organisms. 



In the Mendelian method, the formal relations which exist between 

 hereditary elements are dealt with, particularly their relations in dis- 

 tribution and recombination. The characters of the adult organism are 

 for the most part the basis of judgment. In spite of the general truth of 

 this statement, however, Mendelian analysis has in many cases extended 

 into the field of the physiological relations which exist between hereditary 

 elements, not merely with regard to contrasted homologous hereditary 

 determiners, but with regard to the physiological relations existing in 

 development between entire sets of hereditary elements, and at times 

 even between these and definite factors of environment. But for the 

 most part the solution of such problems depends upon thorough experi- 

 mental study of development in individuals of known genetic constitution. 

 This portion of the problem remains almost untouched. If development 

 be thought of as a series of successive physico-chemical reactions, the 

 complexity of the problem may easily be judged. Certain of the simpler 

 features of it, however, have been attacked and the results of these 

 preliminary studies have indicated still other modes of approach, so that 

 we may expect that when geneticists come to appreciate the light which 

 may be thrown upon heredity by the experimental investigation of 

 development, research in this field will be greatly stimulated. Already 

 as Jennings has pointed out the main features of the process of develop- 

 ment are clearly indicated; the hereditary elements of the chromosomes 

 remain the same in each cell, the reactions and functions of any cell 

 depend upon this chromatin system working in conjunction with the 

 cytoplasmic matrix in which it is located. From this fact may be drawn 

 the broad conclusion that differentiation within the individual depends 

 upon cytoplasm differentiation. The difficulty of the question of how 

 and why should not deter investigation. 



Prerequisites for Genetics. The foregoing discussion of modes of 

 research in genetics should indicate something as to the nature of the 

 working equipment necessary for a study of the science. Since genetics 

 is a biological science, intelligent study of it presupposes a thorough 

 grounding in general biology such as is given in foundation courses in 

 botany and in zoology. Inasmuch as practically all domesticated plants 

 and animals belong to the higher orders, particular attention should be 



