11 
ca. 8000 samples, averaging at the least twice as many specimens. I have also 
preserved several hundreds of specimens in alcohol or formalin and likewise a 
considerable number of samples of stones and the like with incrusted Algæ. Neither 
the conditions nor time have as a rule permitted a more exact examination of the 
collected material at the place investigated; the aim was to keep or at least to 
note all the species present at the single dredging localities. I have however, 
during longer stays at some places on the Danish coasts, been able to make closer 
microscopical examination of fresh material. The main portion of my investigations 
is however based upon preserved material. 
Remarks on the Danish waters. 
As the present work does not intend to give a complete account of the floristic 
conditions nor of all the algal communities, the natural conditions of the Danish 
waters need not be described in detail here, but only the most important points, 
which may serve as a guide for understanding the distribution of the separale 
species and their biological conditions. 
The boundaries of the region. These are partly determined by the poli- 
tical limits. Thus, my investigations extend southward in the North Sea to the 
boundary towards Slesvig, and east of Jutland as far as a line drawn between the 
German and Danish territories thus to the boundary of the region investigated by 
REINKE!. I have made dredgings in the North Sea as far out as the lightship 
on Horns Reef and the eastern side of the Jutland Reef ca. 24 miles from land, 
in the Skagerak ordinarily only to 4 miles from the land except north of Vend- 
syssel where the distance is greater. In the Kattegat my investigations have 
extended to the eastern channel and the grounds in and near it, and in the Sound 
to the deep channel east of Hveen in order to obtain the flora belonging to the 
salt under-current there. The waters surrounding Bornholm constitute a special 
region, which is however connected with the waters east of Mgen by some few 
scattered dredgings. 
The conditions of depth. A general view of these is obtained from the 
charts, which show that a deep channel (the eastern channel) passes from the 
Skagerak southward through the eastern Kattegat, while the water in the western 
part of this sea is relatively shallow. Narrower channels lead further from the 
eastern channel through the Sound and the Belts, of which that through the Great 
Belt is the most important. At Gjedser-—Darsserort this channel meets with a barrier, 
the maximum depth over which is 18 meters, whilst a similar barrier, which has 
a maximum depth of only 8 M., occurs at Saltholm and forms the southern 
boundary of the deep channel through the Sound. South of Schonen the depth 
increases in the Baltic, but becomes specially considerable north and east of 
Bornholm. For the rest, reference may be made to the charts. 
1 J. REINKE, Algenflora der westlichen Ostsee deutschen Antheils. 1889 
