Summary. 
If we go through what has beeu written of the common seaweeds in works 
bearing on this topic, we are struck by the discordancy of opinion as to their 
composition; there is no explanation of this fact, nor can anything be gathered 
from the data given. Shall these plants find a general practical application, and 
accordingly be scientifically utilized for agricultural and technical purposes, an in- 
vestigation into these matters is neccessary. 
After giving an historical survey of the utilization of the seaweed and men- 
tioning the analytical methods used the writer gives an account of the composition 
of the species of seaweed frequently occurring on the coasts of the Sound, 
viz. Zostera, Ulva, Enter omorpha, Pylaiella , Fucus , Ascophyllum, Chorda , Halidrys, 
Furcellaria and Laminaria. It was necessary to examine these plants during differ- 
ent seasons, at different localities with varying external conditions and to distinguish 
between tbe different parts of the plant. The perennials, annuals and ephemerals 
are different in these respects. Upon the whole, however, they have proved to be 
subject to the same conformity of law, but the mode of growth and individual 
qualities give rise to certain modifications. 
It is decisive for the whole nature of the seaweed that it takes its matter from 
the surrounding water in contradistinction to the land-plants which take in most — 
but not all — matters with their roots. As is well known, some of these matters, 
viz. nitrogen and phosphoric acid, occur sparingly in sea-water, whereas the majority 
is to be found there in abundance i. e. all other inorganic mineral constituents, 
except iron. The former are absorbed by the plant during its whole lifetime, but 
as the plant has a time of relative rest in its assimilation in winter and spring, it 
takes advantage of this time to gather a large quantity of these as a reserve matter. 
During the following period of rapid assimilation, in summer, these stuffs are gra- 
dually diluted, and the weed even begins to suffer from the want of them. The 
seaweeds then react differently according to their different modes of growth. 
The absorbtion of nitrogen is done most simply and typically in such a weed 
as Ulva which may partially live through the winter and attains to a rich develop- 
ment later on in the summer. As is shown in the tables VIII, IX, X the absorb- 
tion of nitrogen follows the above-mentioned laws: there is a minimum in the height 
of summer and a maximum in spring before the assimilation quickens. 
