ll 
is a fact which has strongly impressed me from dredgings made in the month of 
January (in the Great Belt and Northern Kattegat). The total mass of algae I 
obtained in the dredge was generally much smaller than im the summer, and I 
received from this the definite impression, that the annual production of substance 
is much more than the half part of the mass which is found in the most luxuriant 
period of the year (early summer). 
In addition to the parts which fall off owing to age, an enormously large 
quantity of parts and whole plants are broken off by outer mechanical forces 
(waves, currents, fishing apparatus). Many of these soon die, but some are able 
to retain vitality, in some cases for years, as they continue to grow whilst dying 
off below. This is what occurs especially in Furcellaria and Phyllophora Brodiær 
on soft bottom-soil in the fjords and other sheltered places. The yearly increment 
of these two algae in the loose condition is perhaps less than half of the substance 
present at a definite point of time, as one can often recognize more than two 
generations of shoots on them; yet it must not be forgotten, that the greater 
number of shoot-generations is possibly counterbalanced by the large amount of 
branching, especially in Furcellaria, which results in most shoots in the last gener- 
ation and in certainly many individuals dying, partly of old age partly because 
they come under unfavourable conditions. So long as definite investigations are 
wanting, it is not possible to say with any certainty how great the annual production 
of substance is in the loose algae, but I do not doubt that the annual production 
in the marine algae, even including the loose algae, is more than the half, and 
probably much more than the half of the algal mass present at any time. 
With regard to the Zostera (grass-wrack), reference may be made to Osten- 
feld's report in the XVIth Report from the Danish Biological Station, 1908. He 
did not come to any decisive result, it is true, but he suggests, that 4 to 6 new 
leaves are produced annually on each shoot. As the number of leaves according 
to his tables varies between 4 and 7, it seems that the leaves entirely or for the 
most part are renewed in the course of one year. To this we must add, that a 
large part of the older plants produce long, flowering shoots, which are entirely 
thrown off after the ripening of the fruit. With regard to the annual production 
of substance the Zostera vegetation can thus be compared with a permanent grass- 
field on land. 
If we were to compare the algae-covered stretches of the sea-bottom with 
plant formations on land, with regard to the amount of production, the comparison 
should rather be with pasture land covered with herbaceous plants, including 
various annuals, but also many shrubs and some low hushes.« 
With this we may conclude our review of the benthos formations in the 
Danish waters. Ås we have seen, the Zostera plays the most important role. 
We may now consider 
The Plankton formation. 
Regarding the plankton in the Danish waters we also find information in 
the Reports from the Danish Biological Station (C. G. Joh. Petersen: Plankton- 
Studier i Limfjorden, Beretn. f. d. d. biol. Stat. 1897, as also De danske Farvandes 
Plankton i Aarene :1898—1901, K. D. Vidensk. S. Skr. 6 R. XII, 3). In 1896 
