58 Arber . — On the Effect of Salts on the Assimilation 
Conclusions . 
The general result of these experiments was that sodium 
chloride, in the absence of other salts, is highly favourable 
to carbon-assimilation, and the presence of this salt alone 
in the medium, if in sufficient degree of concentration, can 
induce a considerable amount, but not quite the maximum, 
of starch-storage. On the other hand, an almost complete 
absence of sodium chloride was found to cause a marked 
inhibition of the carbon-assimilation. It would appear, 
therefore, that sodium chloride is a salt indispensable to Ulva , 
and perhaps to other marine Algae, for the maintenance of 
carbon-assimilation. 
The physiological explanation, which is provisionally sug- 
gested here, is that sodium chloride is a food-substance 
essential to the metabolism of the Alga. It is not of course 
necessary, as Richards 1 has recently pointed out, that a 
substance which by its presence acts as a stimulus to growth 
or carbon-assimilation should be actually used as a food- 
material by the plant. There is, however, some evidence 
from recent research for the view that sodium chloride plays 
a more essential part in the economy of these plants than 
that of a mere stimulus. It is an undeniable conclusion, 
which has served as the starting-point for the researches 
of Schimper and others, that the cell-sap in such plants is 
never entirely free from this salt. Diels 2 , in a recent paper, 
has shown experimentally, that when a Halophyte is cultivated 
in distilled water there is a removal of the contained sodium 
chloride from the tissues. By estimating the quantity of 
NaCl in the ash, he found that 5 grams of the leaf of Cakile 
maritima , Scop., growing on the outer sand-dunes of the 
coast, contained 1*2 per cent. Na Cl. After 5 days’ cultivation 
in distilled water, 5 grams of the leaf contained only -39 per 
cent. NaCl. These results were confirmed by experiments on 
Salicornia herbacea , L. In one case the diminution in the 
1 Richards (’ 97 ), p. 676. 
2 Diels (’98). 
