GENETICS 143 



organs in the constitution of an organism, but they all con- 

 stantly affect and change each other, according to the changes 

 in the central authority. What is more striking is the 

 similarity which the facts of chemical affinities, attractions, 

 combinations, and substitutions bear to the facts of biological 

 (or physiological) affinities and substitutions on the part of 

 certain biological units, behaving as indivisible entities, but 

 even so it does not follow that the organism is reduced to mere 

 mechanism. 



The behaviour of these entities, apparently resembling very 

 closely that of chemical elements, requires some little explana- 

 tion, for it must be remembered that the facts of chemical 

 affinity are still quite mysterious. 



We should like to know the reasons for the strange forms 

 of relatedness of units and of things generally. 



Here the analogy with the plantagens helps us rather 

 more than with the minerals, for we saw the behaviour of the 

 former associated with bio-economic factors, and I believe that 

 the affinities which we are beginning to see in Biology will 

 materially aid us in the interpretation of inorganic combina- 

 tion. Just as we found these bio-economic factors determining 

 the bio-chemistry of life, so these factors will probably be 

 found also at the root of the strange seemingly chemical mani- 

 festations of Mendelian indivisible entities. 



Sometimes these entities will blend and form a genuine 

 (i.e., fixed) inheritance, and sometimes they will not, but split 

 up again and segregate in subsequent generations. They thus 

 behave not unlike plantagens and other symbiotic partners, 

 i.e., under adequate symbiotic conditions they produce a per- 

 manent (sexual) union; i.e., a blend, or, in the alternative, 

 only a transitory and infertile union. 



Of Mendelian "characters" there is, of course, such a 

 promiscuous assemblage that they are bound to be involved in 

 a thousand and one different affinities, and before we can apply 

 the same reasoning as to the plantagens we shall have to sift 

 the grain from the chaff. 



