THE CONSTEUCTION OF PEOTEINS 175 



the luminous ones have a certain feeble effect. Whether 

 or no the energy for the construction is derived therefrom 

 is not, however, certain. 



Sachs held that the sieve-tubes of the nbro-vascular 

 bundles of the axis of the plant are also the seat of the 

 construction of protein. Though this is possible, it seems 

 more likely that they are concerned in the transmission 

 of organic nitrogenous material from the leaves to other 

 organs. In whatever form protein material travels about 

 the plant, which for the present we cannot discuss, it is 

 almost certain that it passes by the sieve-tubes, and it may 

 well be that too great an accumulation of the travelling 

 form may be attended by its conversion into an insoluble 

 condition, and its deposition in the cells. There is no 

 conclusive evidence pointing to the sieve-tubes as the places 

 where it is originally synthesised. 



The same considerations apply to the various growing 

 points or zones. There is little doubt that protein is con- 

 structed there, but it is probable that it is so built up from 

 bodies which have resulted from the digestion or decom- 

 position of protein that has already been synthesised else- 

 where, and which has undergone such decomposition solely 

 with a view to transport or translocation. 



We judge it probable on all these grounds that the great 

 seat of protein construction in a green plant is the leaves, 

 and this not on account of the possession of the chlorophyll 

 apparatus, but because of a property inherent in the cell- 

 protoplasm. Whence the energy is derived is not clear, but 

 many writers hold it to be supplied by accompanying 

 chemical decompositions. 



The construction of protein by fungi is an additional proof 

 that it is altogether independent of the chlorophyll appa- 

 ratus, if not that it is unconnected with the access of light. 



The third group of foods, the fats or oils, are probably 

 not directly synthesised in plants, but are products of the 

 decomposition of proteins, or perhaps of the living sub- 

 stance itself. 



