6 GENETICS IN RELATION TO AGRICULTURE 



sider the opinions which have been entertained by those who have em- 

 ployed this method in the solution of biological problems. Thus Darwin 

 believed that minute continuous variations are transmitted and form 

 a basis for evolution and that the more striking discontinuous var- 

 iations are of little moment in the origin of species. These are beliefs 

 which rigid experimental investigation has failed to establish, and which 

 are, therefore, highly improbable. In fact it has been clearly demon- 

 strated that minute differences between individuals are for the most 

 part not transmitted, and that distinct new characters which appear 

 suddenly are often heritable. Similarly, the inheritance of acquired 

 characters, so readily accepted by men with minds as keen as those of 

 Darwin and Spencer, has failed to receive confirmation when subjected 

 to rigid experimental enquiry. Definite knowledge on points such as 

 these is of tremendous importance in making for progress toward the 

 solution of the general problems of genetics, but such progress is slow 

 and uncertain by the employment of the observational method of attack 

 alone. It is for this reason that the favor of geneticists has swung so 

 strongly toward a more rigid method of experimentation. 



However, the observational method is not unique in possessing limita- 

 tions. No single method is known invariably to give correct results. It is 

 necessary to combine all available methods in order to insure the most 

 certain and rapid approximation to the truth. But the difficulty with 

 the observational method, particularly that part of it known as biometry, 

 has been in the manner of its employment in the elucidation of genetic 

 phenomena. It has been employed, as Pearl points out, both as a method 

 of research and as a method of stating the results of experience. The 

 former manner of utilization is unquestionably of great value in genetic 

 research, its particular value residing in the fact that it has substituted 

 exact methods of expression for vague and indefinite statements. It has 

 performed a service of tremendous value to biology in the introduction 

 of the probable error concept as an index of the degree of reliance to be 

 placed in the results of determinations arrived at by other methods. 

 The latter manner of utilization, however, as a method of stating the 

 results of experience, the employment of which is characteristic of the 

 biometrical school, is subject to serious objections. However, it is worthy 

 of note that the method of observation will ever remain a valuable aid 

 to the extension of knowledge, particularly in directions in which, by 

 their very nature, it is impossible to employ experimental methods of 

 research. It is difficult to imagine, for instance, any notable advance 

 in our knowledge of human heredity save by a proper employment of 

 this method of investigation. 



The Method of Experimental Breeding. The essential feature of all 

 experimental breeding is the raising of pedigreed cultures of plants and 



