376 PHYSIOLOGY 



to divert some of the product into amides by a simple substitution of the 

 amide radical, NH2, for some H or OH radical. Thus, if the fifth group 

 in the glucose chain became HC(NH2), the product would be glucosamin, 

 a substance of quite different properties (see p. 360). Like diversion by 

 substitution might readily occur if only two or three formaldehyde mole- 

 cules had come together. Such processes seem to be the initial steps in 

 protein synthesis (p. 380). 



The common main product, glucose, usually accumulates in the cells 

 because it is formed faster than it can move away. Finally starch or 

 some other stable product appears. The intervening steps are hypo- 

 thetical. It seems that at a certain concentration glucose molecules show 

 a tendency to combine with each other to form a compound sugar, maltose 

 (CioHjjOii), which promptly compounds itself in like manner into a 

 dextrin and finally into starch. The combinations occur rapidly, and 

 the intermediate products are hence obscure. Perhaps the process takes 



place under the influence of third bodies, 

 called enzymes; maltase and diastase in 

 the cases here cited being the possible 

 agents (but see enzymes, p. 399). The 

 Fig. 649. -Two cU^plasts ^^arch accumulates in minute granules 

 ■ of J?Ai/ija/w, with grains of starch within the chloroplasts (fig. 649), SO their 

 (s) and minute oil droplets. — stroma may be the direct agent in organ- 

 izing the starch, or at least may be the 

 seat for the formation of the enzymes which bring this about. These 

 grains have a definite structure and a rather uncertain composition (see 

 starch, p. 358), for both of which the chloroplast itself may be responsible 

 (see leucoplasts, p. 389). 



Removal of products. — If a leaf is isolated, the accumulation of the 

 synthetic products may reach a point where it interferes with further 

 photosynthesis; but in nature this does not occur. Use on the spot, or 

 diffusion of such products as remain simple and soluble, or the digestion 

 of the more complex and the insoluble ones by enzymes (p. 399) and 

 subsequent diffusion, is constantly removing the new materials from the 

 leaves and stems to other places where they may accumulate or be used 

 (see translocation, p. 393). In darkness or weak light, the transporta- 

 tion facilities, temporarily overtaxed in full light, overtake the manu- 

 facturing ; the laboratories are cleared, consumers are supplied, and the 

 warehouses and distributing centers are filled with the surplus awaiting 

 future use. 



