introduction. 5 



subsequent advances have been enormous. Many new sciences, 

 such as cytology, bio-chemistry and ecology, have come into 

 existence, and have made possible an insight into organic structure, 

 constitution and relationship which was undreamed of even half a 

 century ago. 



Just as it is rash to attempt to interpret heredity and variation 

 without a knowledge of the microscopic details of cell and nuclear 

 structure or the physiology of hormones, chalones and enzymes ; 

 so it is equally unsafe to explain many questions of distribution 

 without an intimate knowledge of the ecology and physiology of the 

 organisms concerned. The burden of knowledge laid upon the "}t 

 modern evolutionist is thus so great that no one measures up to the / * 

 possibilities, and it becomes necessary for the worker in one field 

 to obtain second-hand his knowledge of the results in other fields. 

 But it is none the less incumbent upon him to utilize these results 

 intelligently if evolutionary science is to advance. 



This is particularly true of such disciplines as the experimental 

 study of heredity and the investigation of cell and nuclear structure, 

 which had their historical origin in complete independence of each 

 other and have since converged so closely that their results are 

 mutually interwoven. Rarely in the history of science has such a 

 remarkable convergence taken place. Modern genetics represents 

 a synthesis of these two sciences into one. Many genera of plants 

 and animals have now been attacked from both aspects, that of 

 breeding experiments and that of cell structure, with mutually 

 beneficial results ; and it is too obvious to need pointing out that 

 the present position of genetics, both in our knowledge of heredity 

 and of variation, could not possibly have been attained without 

 such combined studies. (Enothera and Drosophila are conspicuous 

 examples but there are many others in the recent literature. In 

 future these two sciences cannot afford to stand alone, but must 

 derive mutual support from each other. Interpretations of breeding 

 results, especially those introducing new complications, which ignore 

 or run counter to well known cytological facts, will have little chance 

 of acceptance. Cytology in its turn will greatly benefit by more 

 comparative studies of related races and species, such as are now 

 being made in a number of plant and animal forms. In such way 

 it is to be expected that a synthetic understanding of genetic 

 phenomena from the combined structural and functional or 

 physiological aspects may be attained. 



