11)06.] on The Physical Bask of Life. 411 



reached, one has to turn to Willard Gibbs's clean sweep of the domain 

 of chemical eciuilibrium. But the author of the Phase Rule hved to 

 see the work rediscovered— again hj a Professor of the University of 

 Amsterdam — and l^ecome the inspiration of a cloud of workers in all 

 lands. The Mendelian laws of heredity, established twenty years 

 earlier, are only now beginning to bear fruit, twenty years after 

 Mendel's death. 



The magnitude of Mendel's achievement can be appreciated by 

 calling to mind the acute intellects which have been foiled by the 

 problem. For a century the study of heredity has remained a repel- 

 lent mass of statistics, with scarcely more discernible order than might 

 be found in any chance collection of facts ; and of the would-be 

 student it might be said, " Qu(esivit ccelo lumen ingemuitque repertay 

 And for half of that century there has lain hidden a solution of the 

 riddle which brings these facts into an order so straightforward that 

 a child might learn it. 



We should have nothing to do with the Mendelian laws here were 

 it not that they have given singular meaning and interest to certain 

 details of cell structure which before were a mere collection of unin- 

 telligent facts. To take things in their proper sequence, I will first 

 state the laws of inheritance so far as thev concern us, and then 

 consider the structural characters Avhich seem to be their material 

 basis. 



The first Mendelian principle which concerns us is this : that what 

 is transmitted from generation to generation may be analysed into 

 certain qualities or characters — constant characters as Mendel calls 

 them — each of which is a unit in heredity, each of which, therefore, 

 is capable of independent transmission. Thus in peas are length of 

 stem, character of inflorescence, colour of seeds, flavour, and so on. 

 Underlying these characters — each of which is capable of being picked 

 out or put back by a breeder, forming a substrate on which they are 

 erected— there would seem to be a basal character which is inalienable 

 and which the breeder cannot, at present at any rate, touch. Thus, 

 in the case of peas, what is of necessity transmitted is the fundamental 

 qualities of " plant " as opposed to " animal," and of " pea " as opposed 

 to other plants. To proceed in Mr. Bateson's words : 



" These [unit] qualities or characters whose transmission in heredity 

 is examined are found to be distributed among the germ cells, or 

 gametes, as they are called, according to a definite system. This 

 system is such that these characters are treated by the cell divisions 

 (from which the gametes result) as existing in pairs, each member of 

 a pair being alternative to the other in the composition of the germ. 

 Now, as every zygote — that is, any ordinary animal or plant — is formed 

 by the union of two gametes [in the process of sexual fertilisation], 

 it may either be made by the union of two gametes bearing similar 

 members of any pair, say two blacks or two whites, ... or the 

 gametes from which it originates may be bearers of the dissimilar 



