THE FOUNDATIONS OF GENP]TICS 275 



Biometry. Many phenomena arc of interest to geneticists 

 whicli are not readily available for laboratory study. Such phe- 

 nomena can be studied by the collection of statistical data. Still 

 other phenomena involve variations which demand much more 

 refined methods of analysis than the mere recording of visible 

 differences, whether studied in the laboratory or in the fic^ld. 

 These conditions have given rise to methods of exact mathemat- 

 ical measurement and analysis which constitute the science of 

 biometry. A knowledge of biometrical methods is not necessary 

 to an understanding of the principles of genetics and the subject 

 will not be treated here. An excellent introduction may be found 

 in Chapter III of Babcock and Clausen's Genetics in Relation to 

 Agriculture. 



An important application of biometry is the determination of 

 the amount of evolutionary change which may have occurred in 

 breeding experiments. Examples may be found in the work 

 cited. 



Summary. The phenomena of adaptation, in order to be a 

 property of species and not merely of individuals, must be handed 

 down from generation to generation. The variations on which 

 they are based are also the materials from which our knowledge 

 of hereditary processes is derived. For the purposes of genetics 

 variations have been classified according to their nature, degree, 

 evolutionary tendency and heritability. Their source is not 

 definitely known, but their immediate origin seems adequately 

 explained by the complexity of the various factors of organic 

 existence. An understanding of the superficial facts of inheritance 

 has long been put to practical use; Galton formulated laws based 

 on such knowledge. The discovery of cells and their behaviour 

 in reproduction has since made possible the correlation of the 

 superficial phenomena of heredity with the morphological basis. 

 Modern genetics also makes use of the established principles of 

 hybridization and selection to provide materials for accurate 

 study. Out of these methods have come definite laws of heredity. 



REFERENCES 



Bateson, Wm., Materials for the Study of Variation, 1894. 



Babcock, E. B. and Clausen, R. E., Genetics in Relation to Agriculture, 1918. 



Castle, W. E., Genetics and Eugenics, 1921. 



Walter, H. E., Genetics, revised edition, 1923. 



Shull, a. F., Heredity, 1926. 



