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. Nosingle method is known invariably to givecorrectresults. 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 
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