478 Plant Physiology 



will it be an exact mean between the two, as a rule, espe- 

 cially where the parents show contrasting characters. It 

 may show distinctive characteristics of both, perhaps some 

 characteristics evident only in more distant ancestors, 

 and others which may seem to have been modified, or 

 which may appear to be entirely new. 



The problems respecting the method of transmission 

 are important, and the theories offered in explanation are 

 both interesting and valuable ; but the physiological 

 picture is as yet more or less indefinite. The evidence 

 derived from a minute study of the cell, or cytology, may 

 be of assistance, but it is not to be expected, in general, 

 that any single characteristic of the organism will leave a 

 special morphological imprint upon the nuclear structure. 



291. The early studies. - The early studies upon 

 heredity yielded many valuable observations, yet they 

 were disappointing with regard to definite results and to 

 the development of special methods for attacking the 

 general problem. Kolreuter, Knight, Gartner, and others 

 accumulated interesting data. Galton employed statis- 

 tical methods, and his studies of pedigree records led him 

 in 1897 to announce his famous " law of ancestral heredity." 

 By this hypothesis, assuming unity as the total hereditary 

 possession of any organism, he assigned diminishing values 

 in a geometrical series (the total approaching unity) to 

 the ancestors in preceding generations, from parents to 

 those more remote, averaging as follows : parents one half, 

 grand-parents one fourth, great-grand-parents one eighth, 

 etc. This conception may be regarded, perhaps, as an 

 expression of the practical results of complex hereditary 

 influences, through many generations ; but from it we seem 



