6o Arber . — On the Effect of Salts on the Assimilation 
that sodium chloride acts as a controlling agent, but I am 
inclined to think that the large amount of the removal of 
Na Cl from the leaf, as found by Diels, and the extreme 
importance of this salt as shown here, are strongly in favour 
of the view that in such Halophytes as Ulva the Na Cl is 
also essential for the metabolism. Whether it is the acid or 
the base, or both, which is necessary, is a question which 
only further work can answer. 
Lastly it is interesting to contrast the results obtained with 
Ulva with the conclusions which have been drawn from non- 
halophytic Phanerogams. Schimper 1 has concluded that for 
the great majority of plants Na Cl is of no importance as 
a food material, and further that in salt-solutions the assimi- 
lation is inhibited to such a degree that starch and sugar are no 
longer produced. Stahl 2 , Lesage 3 , and Dassonville 4 , among 
others, have also concluded that salt-solutions tend to injure 
or diminish the carbon-assimilatory apparatus. Richter 5 
has however pointed out that these results do not necessarily 
hold in the case of freshwater Algae. 
Section VI. Other Chlorides in Sea water. 
Besides NaCl, two other chlorides — magnesium chloride 
and potassium chloride — occur in sea water in the proportion 
of o»3 per cent, and 0*07 per cent, respectively. Potassium 
is an essential element to all plants, and in case of Ulva is 
derived entirely from the small proportion of KC 1 in sea 
water. Magnesium is also essential, and is obtained from the 
chloride, sulphate, or the very small amount of nitrate in 
sea water. Experiments were made in which Ulva was ex- 
posed in a solution made up of distilled water and all the 
principal salts of sea water in the proportions which they 
there occur, with the exception of MgCl 2 in one case, and 
K Cl in the other. The absence of either salt did not seem 
to affect the amount of starch formed in any way. 
1 Schimper (’98), p. 98, and (’91), p. 26. 
3 Lesage (’90). 3 Stahl (’94), p. 136. 
* Dassonville (’96). 5 Richter (’92). 
