THE CONSTRUCTION OF PROTEINS 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 fibro-vascular 
bundles of the axis of the plant are also the seat of the 
construction of protem. 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 ig 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 ig altogether independent of the chlorophyll appa- 
ratus, if not that it ig 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. 
