NUTRITION 393 



lated to one another in amount as to form what animal feeders call 

 a balanced ration. This is shown by the fact that, when growth is 

 resumed, food of one sort is not used in the ratio which it bears 

 to others stored with it. Often indeed the reserves are not exhausted 

 until the plant or shoot, having begun independent manufacture, is able 

 to supplement the deficiencies in the stored ration. Thus, finally, it 

 may utilize all the accumulated reserve, but often this is not done, and 

 the excess is again stored elsewhere. 



Traveling forms. — Since the places of storage are seldom the places 

 of food making or use, translocation of food usually precedes and fol- 

 lows storage. Unfortunately, little is known about the translocation 

 of foods. It seems clear that the traveling forms must be relatively 

 simpler than those in which they are stored. Obviously, they can travel 

 only in solution, and, as a rule, the protoplasm does not permit the pas- 

 sage of the foods in their storage forms. Thus, cane sugar probably 

 travels as glucose and fructose; the fats as glycerin and fatty acids; 

 the proteins as amides. For in all translocation of foods, whether in 

 small plants or large, it is necessary that they be able finally to diffuse 

 through live cells, and the more complex compounds are usually un- 

 able to do this. 



Diffusion. — In the smaller plants osmotic differences alone must 

 account for the transfer from cell to cell. This may be facilitated by 

 the delicate protoplasmic connections which commonly exist and would 

 make it unnecessary for all the food to pass through the cell wall itself. 

 In fungi which have coenocytic hyphae, the absence of transverse parti- 

 tions probably facilitates transfer ; while the surging movements that 

 have been observed in the contents of certain molds (Mucorales) would 

 certainly do so. Yet actual knowledge regarding the translocation of 

 food in even the simplest plant is scanty. Food obviously gets from 

 place to place, and there is apparently no way for it to do so except by 

 diffusion. 



Conducting system. — In the larger plants a conducting system is 

 developed; and it is evidently advantageous that the slower movement 

 of diffusion be supplemented by a more rapid one along the chief lines 

 of travel when the factories are separated by considerable distances from 

 the places of use or storage. This conducting system in all the vascular 

 plants consists of the phloem strands. It may be supplemented in 

 certain large families by the latex system, though the function of the latex 

 is somewhat uncertain. 



