1904 - 5 .] Study of the Lakes of Scotland and Denmark. 40 3 
the investigations relating to the extremely interesting plankton, 
the bottom-fauna, the Diatom flora of the shores, and the influence 
of water rich in humic acid upon fresh-water organisms, may be 
studied in accordance with the knowledge which has been gained 
of the life-conditions common to all organic life. It would be 
most unfortunate for the study of fresh-water and its organisms if, 
in a country where the knowledge of the life-conditions is so 
prominent, this knowledge should not be fully utilised. 
During the last fifteen years I have spent most of my time in 
the study of our own lakes and their organic life, and I hope 
that my statements in the following condensed and brief account 
of the Danish lakes may prove reliable ; time will show whether 
I have carried my generalisations too far. What I learnt re- 
garding the Scottish lakes brought to light many differences 
between them and our own lakes ; and I had occasion to make 
some observations which, if carried further, would have served 
as starting-points upon which to base my working theories. My 
knowledge of the Scottish lakes is, of course, very limited, but I 
hold it to be the duty of a scientist not only to make known the 
actual facts observed by him, but also his ideas as to the bearing 
of these facts. Strictly speaking, new ideas should be regarded 
not so much from the standpoint as to whether they may be 
right or wrong, but rather as to their value in the promotion of 
scientific knowledge ; and I hope the following pages may contain 
ideas useful in some measure in future investigations. 
I. 
General Remarks on the Natural Conditions of the 
Danish and Scottish Lakes. 
A. The Danish Lakes. 
My explorations have shown the most remarkable differences 
between the Danish and the larger Scottish lakes in nearly all par- 
ticulars, which was to be expected, considering the wide divergence 
in the geological structure of the two countries. I would here 
merely point out that Denmark is a lowland country, the highest 
eminences not exceeding 500 to 550 feet above sea-level, and, 
