BEHAVIOR AND FUNCTIONS OF THE NUCLEUS 297 



coalesced, and the nodes in the right-hand fragment without the 

 primordium nevertheless fused simultaneously with those of the 

 other fragment which carried the developing anlagen. Similarly, 

 if stage-6 dividers were cut in the same way so that the clumped 

 nucleus remained in the fragment without the primordium, the 

 nucleus then extended and renodulated on time (Fig. 84). Such 

 observations suggest that the nucleus is guided in its behavior by 

 something which characterizes the whole cell rather than by 

 stimuli emanating exclusively from the primordium. 



7. Necessity of the nucleus for oral redifferentiation 



No experiment demonstrates more dramatically the fundamental 

 duality of the cell than the failure of Stentor and other ciliates to 

 regenerate or survive without the nucleus. The nucleus cannot 

 regenerate a cytoplasm around it and is indeed so dependent upon 

 its cytoplasmic environment that naked nuclei soon degenerate 

 and cannot viably be returned to the cell. Likewise cytoplasm 

 alone can never produce a nucleus. Specifically in regard to Stentor, 

 our starting point in the study of nucleo-cytoplasmic interactions 

 is that oral regeneration or the formation and development of a 

 primordium is a cooperative effort of nucleus and cytoplasm and 

 does not occur in the absence of some portion of the macronucleus. 



Yet the nucleus does not make the primordium in the sense of a 

 handicraft but remains visibly unchanged while the anlage is 

 elaborated at some distance from it. Hence there should be some 

 intermediate step through which the nucleus contributes to the 

 support of primordium formation in the cytoplasm. This inter- 

 mediary would be truly essential to redifferentiation ; the presence 

 of the nucleus only indirectly as its source. Such a relationship is 

 evident in the amazing case of the unicellular plant Acetahularia 

 (see Hammerling, 1953) in which both growth and the elaboration 

 of specific organelles continues long after enucleation, in a way 

 that can best be explained by supposing that the nuclear contribu- 

 tion is a durable substance which persists, quantitatively, in the 

 cytoplasm until exhausted. 



If the action of the nucleus is indirect and mediated through 

 products which it contributes to the cytoplasm, there should also 

 be some evidence of this lag-effect in Stentor. Using coeruleus as 

 the test organism, I have found (unpublished) that the oral 



