480 



PLANT GROWTH AND PLANT COMMUNITIES 



Figure 11. Cross-sections of the cotton hair, showing the hair's strongly 

 lamellated structure (10), which disappears if growth occurs under constant 

 environmental conditions (11) but is restored by experimentally-induced 

 diiu-nal variations (12). (From Anderson and Kerr, 1938.) 



If the living system intervenes in so many ways, through factors 

 operating both from within and without, to determine the architecture 

 of so relatively simple a product as cellulose, built essentially of 1-4 

 /?-glucosidic links, how much more may this apply in the case of such 

 complex substances as protein? The point here is that the controls are 

 neither solely genetic nor inherent in the enzymes that produce the 

 chemical syntheses per se, for there must also be obvious controls 

 which operate at the macromolecular level, and these can only be re- 

 garded at present as essentially part of that complex which we recog- 

 nize as organization in the cell and the organism. 



Although the above example was drawn from cellulose, a similar 

 argument could be constructed for starch. Phosphorylase may unite 

 glucose-1-phosphate to form the 1,4 a-glucosidic links and this, with 

 the "branching enzymes," may determine whether chemically recogniz- 

 able amylose or amylopectin is formed, but the morphological struc- 

 ture of the starch grains, which is characteristic even of species of 



