TBANSLOCATION OF NUTEITIVE MATEKIALS 221 



when the conditions of carbohydrate 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 carbo- 

 hydrates, 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 amino- or 

 amido-acid such as asparagin. This view is supported 

 by observations made upon the utilisation of the reserve 



