360 The Unity of the Organism 



of a given pair to the other chromosome of that pair. 



So rapidly have come the striking observations in this 

 field, and so striking have been the theoretical interpretations 

 set forth that many biologists who have been admiring on- 

 lookers, have seemingly failed to discriminate just how much 

 of what has been presented is fact, how much legitimate in- 

 ference, and how much hypothesis in the strict sense. It is, 

 consequently, eminently fortunate that Morgan himself has, 

 as noted above, given us an explicit even though an inade- 

 quate statement of how the case stands in this regard. The 

 sentence quoted some pages back, "We have made no as- 

 sumptions concerning heredity that cannot also be made 

 without the chromosomes as bearers of the postulated hered- 

 itary factors," : 2 should be recalled. The case standing 

 thus, the present discussion would not be furthered by going 

 into more of its details. 



And so we come to the end of our examination of the 

 observational evidence favorable to the theory that heredi- 

 tary attributes in bisexually propagating organisms are in 

 some way and to some extent dependent upon the chromo- 

 somes of the germ-cells. The conclusion must be, it seems, 

 that not many of the major theories in biology are more se- 

 curely established than this. Thus stated, the chromosome 

 doctrine not only takes its place along-side the cell-doctrine, 

 but it supplements, and in fact, partly supplants the cell 

 doctrine. Never again, for example, can the cell be con- 

 ceived, as many earlier cellular elementalists were wont to 

 conceive it, as The Ultimate Unit of organic beings. 



In several instances presented by the foregoing review of 

 the chromosome theory of heredity, notably in that of the 

 pollen grains of flowering plants where the final act in fer- 

 tilization appears to be accomplished by the chromatin alone 

 (see p. 343), the chromatin manifestly constitutes a unit 

 beyond the cell and hence nearer to ultimateness than is the 

 cell. 



