306 



Gene Action 



As shown in the third section of Fig. 85, Wright has suggested 

 that special genes in the nucleus may produce model nucleo- 

 proteins which migrate into the cytoplasm, where they retain 

 their genie property, although this property is subject to decay, 

 at least along the germ line. These model nucleoproteins then 

 duplicate themselves many times in the cytoplasm and thus 



NUCLEUS 



CYTOPLASM 



HEREDITY 



Nutrients i i i i i 



Nucleic Acid 

 Protein 



Nucleic Acid 

 Protein 



METABOLISM 



Nutrients- 



Nucleic Acid 

 Protein 



-♦Substrate- 



Prosthet ic 

 Group 



7 



I Enzyme I 



• Product 



GROWTH 



Nutrients ; i i i a 



Nucleic Acid 

 Protein 



Nutrients 



rrnr 



Nucleic Acid 

 Protein 



Nucleic Acid 

 Protein 



DIFFEREN- 

 TIATION 



Gene 



Nutrients - 



Gene 



TTTTT 



Plasmagene 



Moditied__ 

 Plasmagene 



Modified 

 Plasmagene 



■*■ Substrate | > Hapten 

 1 i i i t' [Enz.vme| 



Plasmagene 



Fig. 85. Wright's scheme of gene action. 

 (After Wright in the American Naturalist.) 



For explanation, see text. 



build up the large numbers of proteins necessary to produce 

 a new cell by cell division. 



A suggestion concerning the way various cells become dif- 

 ferentiated is given in the lowest section of Fig. 85. This scheme 

 seeks to throw light on the problem of how a simple, undifferen- 

 tiated cell in one particular region becomes a tracheid while 

 another one near it becomes a parenchyma cell, a fiber, or a cell 

 of the phloem. Our knowledge is by no means complete, but 

 there is considerable reason to believe that this differentiation 

 has a cytoplasmic basis. Wright's suggestion is that the cyto- 

 plasmic differences which cause cells to differentiate into cells 

 of different shapes, sizes, and functions result from a controlled 

 mutation of plasmagenes. As Fig. 85 shows, plasmagenes are 



