Heredity 201 



a new conception of the proximate mechanism of heredity, 

 although it does not represent a complete hypothesis of 

 heredity, since it begins with the gametes after they are 

 formed and does not account for the constitution of the 

 gametes, nor the way in which the parental characters 

 are impressed upon them. This hypothesis focuses our 

 attention along new lines, and will arouse more discussion 

 than Weismann's hypothesis did ; and it will have a much 

 wider influence. Whether it expresses the actual means 

 of heredity or not it is yet much too early to say ; but 

 this hypothesis is a greater contribution to science than 

 the so-called "Mendel Law" as to the numerical results 

 of hybridization : the hypothesis attempts to explain the 

 "law." 



One great merit of the hypothesis is the fact that its 

 basis is a morphological unit, or at least an appreciable 

 unit, not a mere imaginary concept. This unit should be 

 capable of direct study, at least in some of its phases. 

 It would seem that the mendelian hypothesis would give 

 a new direction to cytological research. 1 



It is yet too early to say how far Mendel's law applies. 

 We shall need to restudy the work that has been done 

 and to do new work along more definite lines. There 

 are relatively few former results or experiments that can 

 be conformed to Mendel's law, because the data are not 

 complete enough or not made from the proper point of 

 view. We should expect the fundamental results to 

 be masked when the plants with which we work are 



1 See, for example, "A Cytological Basis for the Mendelian Laws," 

 Bull. Torr. Bot. Club, 29, 657 (1902), by W. A. Cannon; and other 

 papers of this kind. 



