360 BOTANICAL GAZETTE [MAY 
characterized only by its constant relation to the outer world, and the author 
believes any other definition is artificial and arbitrary. More explicitly, a 
species is defined as comprising all those individuals which have arisen by 
vegetative ee or by self fertilization, and which for many generations 
r like conditions have shown identical characters. This definition is not 
arbitrary to a reviewer, provided the assumption of a specific structure upon 
which it rests is not arbitrary. If by definition potencies can never transgress 
the limit prescribed by the specific structure and variation is merely the expression 
of potencies, how have species arisen by variation? The potencies of the author 
are merely inherent capacities to respond to certain combinations of external 
conditions and are purely immaterial as compared with the pangens of DE VRIEs, 
“which are material and carry the unit characters. To some investigators this 
discrimination will probably appeal as being an interpretation closer to nature 
and more logical from the strictly physiological standpoint. To others it may 
seem as merely a restatement of the conception of DE Vries. The latter might 
easily inquire what difference it makes whether a given variation has arisen by 
an inactive pangen becoming active or by a hitherto impotent potency becoming 
potent——Raymonp H. Ponp. 
The lakes of Scotland and Denmark.—At the invitation of Sir JoHN MuRRAY 
Dr. C. WESENBERG-LUND'S spent three or four weeks on the Scottish wie 
in order to make a comparison with the lakes of Denmark. ile this was a 
short time in which to make examination of a new country nevertheless we should 
expect interesting results from one who has not only accomplished so much 
thoroughly good work in the study of lakes, but has shown unusual skill and 
originality in his interpretations. 
The -general differences which the author finds between the Danish and 
Scottish lakes are the differences which we should expect between shallow and 
deep lakes. The Danish lakes have more plankton, more floating and sub- 
merged vegetation, and more distinct littoral zones of vegetation. The greater 
seasonal variations in the Danish lakes is noted; this, of course, would be 
expected from the greater variations in temperature. There are more highly 
colored crustacea in the Scottish than in the Danish lakes. The reviewer thinks 
the author right in correlating this red color with low temperature, rather than 
with elevation as has been done by some other authors. 
Among the diatoms the author notes the absence of Melosira and Steph- 
anodiscus in the Scottish lakes, with an abundance of Asterionella and Tab- 
ellaria. These facts compare well with the differences in America between 
the deep and shallow lakes. The Scottish lakes are remarkable for the large 
number of desmids. These desmids are of forms that are common in the pools 
of the hillsides. The occurrence of these desmids in the plankton, together 
«5 WESENBERG-LuNp, C., A comparative study of the lakes of Scotland and 
Denmark. Proc. Roy. Soc. Edinburgh 22: 401-488. pis. 2. 1905 
