THE CONSTRUCTION OF PROTEINS 173 
reduced by the formaldehyde, part of which combines with 
the resulting product to form hydroxylamine and later 
formaldoxine, which is then converted into formamide. 
The view of the construction of protein from amido- 
compounds and carbohydrates, though of course only 
hypothetical, associates certain processes which apparently 
occur in nature. Its formation seems to involve the simul- 
taneous presence in the cells of some amino- or amido-acid, 
frequently asparagin, and some carbohydrate such as sugar. 
If shoots of plants which exhibit no accumulation of asparagin 
during normal growth are cut off and kept in darkness for 
some time, a gradual accumulation of the amido-acid can 
be observed. This in all probability is the expression of 
the decomposition of protein taking place during the life 
of the shoot, and is presumably a normal occurrence. The 
reconstruction which would explain its non-accumulation 
during illumination is prevented by the non-formation of 
the needed carbohydrate in the darkness. 
The probability of a combination or interaction of these 
two classes of substance in the synthesis of proteins is 
supported by the fact that at the active growing points, 
where protoplasm is energetically formed, and where con- 
sequently abundant supplies of proteins are needed, neither 
sugar nor amido-acids can be detected, though they can 
be traced quite readily up to a short distance below the 
place where this active growth is proceeding. This fact is 
easily understood if we admit that protein is constructed 
there at the expense of these two constituents, supplemented, 
of course, by the necessary compound or compounds of 
sulphur. If either of these supplies ceases to be available, 
the growth of the plant at that point stops. 
Though we have seen reasons for thinking that nitrates 
and amido-acids form two stages in the normal process of 
protein construction, we must not conclude that they in- 
variably do so. In one plant, Pangiwm edule, which was 
examined by Treub in 1894, the nitrogen needed for protein 
construction appears to be supplied in the form of hydro- 
~ eyanic acid. In the shoots of this plant, cells occur in the 
