Nature of Heredity and Problem of Mechanism 307 



conducted under tin- guidance of Mendel's discoveries, on 

 the- other, have almost if not quite demonstrated some sort 

 of interdependence between the chromosomes of the germ- 

 inal cells of several species of sexually propagating plants 

 and animals, and such attributes of adults. These demon- 

 strations are perhaps the most important achievements of 

 biology in the last decades, and they must ever hold high rank 

 in the history of the science. 



How do the new discoveries appear when viewed from the 

 organismal standpoint? A study of recent writings on 

 heredity gives one the impression that elementalist concep- 

 tions have left cells behind and passed on to chromosomes, 

 elements which lie at a deeper level as one might express it, 

 of organic constitution than do cells. Much recent discus- 

 sion of the mechanism of heredity has not been cytologftal 

 so much as chromosomological. Somewhere in the first 

 few pages of nearly all semi-popular books on genetics one 

 finds diagrams of the egg-cell witli the nucleus and its chro- 

 mosomes represented in due particularity, but with the body 

 of the egg left blank, the implication being that this part 

 contains nothing significant for heredity. So much has 

 recent thinking on the "hereditary substance" kept chro- 

 mosomes in the foreground as "carriers of heredity" that 

 the most radical elementalists might, quite- conceivably) grant 

 that the main mass of each cell, whether germ-cell or soma- 

 cell, may be an organ and so subject to the organism, yet 

 contend that the chromosomes are not so subject. In fact, 

 spec-illations like those recently published by the late K. A. 

 Minchin on the evolution of the cell appear to claim just 

 this sort of primacy for chromosomes, or at any rate for 

 chromatin. 



