Cook: Reticular Heredity 



345 



be considered more strange that a 

 character should continue latent for a 

 series of generations than that a seed 

 shoiild lie dormant for a period of years, 

 expressing none of the characters of 

 the plant, and yet losing none of them. 



What we call characters may be, 

 after all, only phases or stages in the 

 development of the organism and may 

 not be embodied in the protoplasm in 

 any such manner as the corpuscular 

 or genie theories have assumed. The 

 larva or the embryo, the egg or the 

 spermatozoon, is as truly an organism 

 as the adult. Each form of life has 

 its complete cycle and it is only an 

 artificial, mechanical analogy that leads 

 us to think of one part of the life-cj^cle 

 as less complete than another. The 

 cycle being continuous, each part can 

 be considered as a preparation for the 

 next, but in the very nature of the case 

 there is no beginning or end. 



If the idea of transmission seems to 

 involve the notion of embodiment of 

 the characters in the protoplasm of the 

 germ-cells, we should see that this is 

 only a deduction from the preconcep- 

 tions with which we have approached 

 the subject, and that it affords us no 

 additional insight into the process of 

 transmission. Until we have a working 

 knowledge of the constitution of the 

 protoplasm itself, the nature of the 

 process of transmission can only be 

 inferred from the facts of expression. 

 Any inferences that may be drawn 

 regarding the numbers and relations 

 of the gens must accord with the be- 

 havior of the visible characters, and 

 must accommodate the facts of heredity 

 in networks of interbreeding lines of 

 descent in natural species, as well as in 

 single lines of descent in specially pro- 

 pagated domesticated varieties. 



Domestication has been supposed to 

 change the characters of plants and 

 animals by placing them under different 

 environmental conditions, but this factor 

 is probably much less important than 

 changes in the methods of descent. 

 Where domestication has not been 

 accompanied by restriction of descent, 

 the normal state of individual diversity 

 has not been lost, or given place to the 



greater diversity between narrow bred 

 strains. In such cases as the rye plant 

 or the Guinea fowl, where narrow 

 breeding has not been practiced, the 

 whole species remains relatively uniform 

 and stable, in comparison with the 

 species where descent has been restricted 

 to narrow groups or to individual 

 lines. 



COHERENCE OF CHARACTERS. 



Merely increasing the numbers of 

 gens does not fully provide for the fact 

 that many characters are usually 

 changed together instead of one char- 

 acter at a time. Even assuming that 

 there are many alternatives for each of 

 the features of a plant or animal, there 

 would still be no reason why the sub- 

 stitution of one of these alternatives for 

 another should be connected with 

 changes among the alternative gens of 

 other characters. Our ideas of re- 

 lations of the gens to each other have 

 to be modified, in addition to recog- 

 nizing increased numbers of gens. If 

 we think of characters as representing 

 stages and alternative courses of de- 

 velopment, the gens, as predetermining 

 rudiments of the characters, must be 

 thought of as having intimate mutual 

 relations, instead of being considered as 

 entirely independent. 



The tendency of characters to segre- 

 gate or behave as independent entities, 

 as manifested in typical Mendelian hy- 

 brids, is often counteracted by an op- 

 posite tendency to coherence or associat- 

 ed expression of characters. When the 

 tendency to coherence is strong a whole 

 series of characters may behave more 

 or less like a single Mendelian unit, so 

 that examples of coherence are often 

 reported as cases of Mendelism.^ 



It may be nearer the truth to say that 

 organisms different in one respect are 

 different throughout, than to make 

 the Mendelian or monogenic assumption 

 that characters are separate entities 

 to the extent that one character can be 

 changed without affecting the others. 

 The idea of alternative courses of de- 

 velopment is in better accord with the 

 general facts of biology than the idea of 

 alternative gens, as shown by the 



^Cook, O. F., Mendelism and Interspecific H\'brids, American Naturalist. 



