Studier öfver svensk tång, företrädesvis från Öresund 
49 
Zostera with perennial rhizomes economizes the small quantity of nitrogen to 
be found in the water in such a way that the roots and the tender autumnal leaves 
begin in November to take in stores of nitrogen, and the quantity of this substance 
increases in winter and spring in order to be able to supply the leaves and stalk 
with it during the rapid assimilation in summer. The quantity of nitrogen practic- 
ally experiences the same changes as in Ulva, cf. table V, even though it never 
rises to such a height as in this specially nitrogenous plant. Judging from the few 
analyses made, cf. table XXIV, the conditions are the same in the case of Laminaria: 
its stipe and remaining part of thallus correspond to the roots and new leaves of 
Zostera. Äs to the perennial brown algae whose thallus wholly remains, the case 
is more complicated. The absorbtion of nitrogen has been most carefully examined 
in Fucus vesiculosus. The yellow annual shoots developed in summer have a notable 
capacity of gathering nitrogen from their surroundings, while the older thallus al- 
most gets independent of the season, and there is no change at all in the compo- 
sition of the stipe. As is more fully shown in table XIII, the new shoots get richer 
in nitrogen late in autumn, and then the quantity increases until late in spring 
when new shoots, poor in nitrogen, are again developed from the old ones. Fucus 
serratus, Ascophyllum , ffalidrys and Fnrcellaria present a quite analogous state of 
things, as is seen by the analyses, cf. the tables XVIII, XX, XXII. The annual 
Chorda grows slowly in spring and then finds time to gather some store of nitrogen 
to last it for the summer; owing to the rapid assimilation, however, a dilution takes 
place during this time, whereas late in autumn a new store of nitrogen can be 
taken in before the plant dies. The ephemeral algae which have been examined, 
Enteromorpha and Pylaiella, are like the annuals, cf. table XXV. 
The total variations of the quantity of nitrogen extend between 1 to 4.5 per 
cent., yet different in different plants. Ulva is richest and the annual Chorda 
poorest in nitrogen. 
The quantity of phosphoric acid in these plants is throughout very small i. e. 
varying between 0.1 and 0.7 per cent. It varies in the same manner as nitrogen ; 
still there is no definite relation. Here too Ulva stands foremost. Its comparatively 
high percentage of phosphoric acid is explained by the fact that it only occurs in 
water abundant in nutriment. While in the land-plants N : P 2 0 5 is found in the 
proportion 2:1, the proportion is here 5:1. 
The quantity of iron follows — in the chlorophyll-carrying seaweeds at least 
— that of nitrogen and phosphoric acid, the largest quantity in Ulva and Zostera 
being found in winter and in spring. In the brown algae the quantity of it is 
small and less varying. 
The other mineral matters, viz. the salts of K, Na, Ca, Mg with Cl and H 2 S0 4 
that occur plentifully in seawater, are at the disposal of the plants in exceedingly 
large quantities, and therefore there is no need for them to gather more of these 
matters at a given time, than is necessary for producing an even osmotic pressure. 
The quantity of these substances is very large, i. e. about 15 per cent. There seems 
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