6y8 Arber. — On the Effect of Nitrates on the 
Percentage Percentage 
in sea-water. in total ash of 
various Fucaceae 1 . 
Iron 0-0005 0-29-0*34 
Combined nitrogen 0-0002 
Iodine, less than . o-ooooi 0-31-1-13 
Phosphorus . . . 1-36-4-4 
With regard to phosphorus, no chemical analysis of sea water 
contains any estimation whatever of that substance ; the 
trace being infinitely small 2 . Noll 3 has drawn special atten- 
tion to this in a paper on the culture of marine Algae. The 
same author 4 regards iodine, which occurs in an almost 
equally small proportion, as not indispensable to Algae. The 
necessity of iron was first pointed out by Gris 5 in 1843, and 
his are probably among the earliest observations, which 
showed that an inhibition of the carbon-assimilation in a 
plant can be caused by the absence of an essential inorganic 
salt. Molisch 6 has found, and it is generally admitted, that 
the molecule of chlorophyll does not contain iron, and it 
is therefore highly probable that iron is essential to the 
metabolism of the chloroplast. It would seem, therefore, that 
in sea water we have certain essential elements, in what is 
probably the smallest degree of concentration ever made use 
of in nature by plants, A better illustration of the selective 
capacity of the plant, and its power of absorbing substances 
in direct proportion to the amount necessary for metabolism, 
and in altogether disproportionate amount to the ratio of the 
substances in a given volume of the medium, would be hard 
to find. 
The Starch-accumulation in Marine Algae. 
One point, which has been very prominent throughout 
these experiments, is the large accumulation of starch which 
occurs in these Algae, and the very slow rate of translocation. 
1 Goedechens, vide Pfeffer (’ 00 ), p. 128. 
3 Noll (’ 92 ), pp. 282-3. 
" Gris (M 4 ). 
2 Voelcker (’ 50 ), pp. 346-7. 
4 Noll (’ 92 ), p. 285. 
6 Molisch (’ 92 ). 
