326 WILLIAM LAWRENCE TOWER. 



there are activities of the cell ; neither is it necessary to suppose 

 a different substance present for every independent factor identi- 

 fied. The various independent factors may have a basis no more 

 complicated than that of so many atoms attached to a complex 

 molecular structure. Experiment shows that the factors may 

 be detached one by one from the organic complex. The discontin- 

 uity of their coming and going is entirely in harmony with the 

 conception of them as components merely of complex molecular 

 bodies." 



If I understand Castle correctly, the atoms or groups thereof 

 that are detached, are not of themselves the repository of capaci- 

 ties such that anywhere they would produce a given result, but 

 rather, because of their absence in the complex group, the de- 

 velopment of a character fails, and their presence is necessary 

 to the appearance of the character in question. This conception 

 is fundamentally different from the representative particle ideas 

 of DeVries or Weismann, although the two ideas are not in- 

 frequently confused. 



In the introduction (p. i) I pointed out that the fundamental 

 question which must be answered before we can get any real expla- 

 nation of Mendelian behavior is, whether these "unit characters," 

 are lesser entities conditioned by representative particles capable of 

 mosaic rearrangement in the organism. It was further pointed 

 out that to conceive of an organism as an entity analogous to a 

 crystal, or as a mosaic more or less analogous in certain respects 

 to granite or to orthoclase-feldspar crystals, expresses figuratively 

 some of our experiences concerning the nature and composition 

 of organisms. 



There is, unquestionably, in all organic forms that which has 

 the stability of form characteristic of crystals, and there is that 

 which can be removed or replaced without in any way changing 

 the basic form, exactly as impurities can be removed from or 

 substituted for in crystals. Likewise, there are alternative con- 

 ditions of existence of this basic form, which, like allotropic 

 crystals, can exist only as one or the other form. 



In germ cells the colloidal ground substance, which Lillie (1906, 

 1909) finds is not disturbed in its polarity and in its future de- 

 velopmental processes by powerful centrifugal force, may very 



