TRANSLOCATION OF NUTRITIVE MATERIALS 215 



hydrate formation are realised, that it may be relied on as 

 a test for the absorption of carbon dioxide by the tissue in 

 which it appears. 



In connection with the manufacture and fate of carbohy- 

 drates, we can now see that they may be met with in two 

 different conditions : the one suitable for retention in the 

 cell and hence capable of functioning as reserve, but not 

 immediately nutritive, material : the other capable of 

 diffusion, and hence serving as a translocatory form, or 

 one in which it can pass from cell to cell, remaining all 

 the time in a suitable condition to minister to the nutrition 

 of any protoplasm which it reaches. 



The same considerations affect the manufacture, trans- 

 port, and storage of proteins. We have already seen 

 reason to believe that these, like the carbohydrates, are in 

 the first instance constructed in the leaves, if not by the 

 chloroplasts. Our information about them is, however, 

 very incomplete ; we do not know even what form of 

 protein is first formed, nor which kind is needed for 

 assimilation by the protoplasm. Possibly it is a soluble 

 and diffusible form, such as a peptone or a proteose, but 

 our only reason for thinking so is that such properties 

 characterise the travelling forms of carbohydrates. We 

 can, however, readily believe in the construction being 

 greatly in excess of the immediate need of the cell, and 

 hence in the chain of events being similar to that in 

 which the carbohydrates are concerned. 



The different properties of the two classes of bodies 

 involve, however, some differences in their behaviour, 

 and we can therefore expect similarity only and not iden- 

 tity. The diffusibility of peptone even is very greatly 

 below that of sugar ; and we can hardly suppose therefore 

 that peptone is the translocatory form of protein in the 

 plant. It seems more probable that nitrogenous plastic 

 material is transported in the form of some ammo- or 

 amido-acid such as asparagin, and that the latter is subse- 

 quently worked up into protein at the place where it is 



