396 THE FRESH-WATER LOCHS OF SCOTLAND 
for the Scirpiis-Phragmites growths especially are in numerous cases 
not present ; on the other hand, the outermost vegetation belts, 
especially the Characece, with a fairly well-marked Nitella zone of 
13-30 m., reach much greater depths than in the Baltic lakes (Lake 
of Geneva and Bodensee.) The higher we go up the mountains the 
more the importance of the vegetation belts as nutrition for the 
animals decreases (Zschokke, 1900, p. 14). In lakes above 1600 m. they 
generally play a secondary part. Yet Potamogeton^ Sparganmm, and 
especially Batrachnmi grow as high up as 2100-^500 m. A very great 
part of the vegetation in the high alpine lakes is for the rest made up 
of Characeae ; where these are absent Confervaceae, Diatoms, and 
Desmidiaceae, in addition to the phytoplankton, are in the majority ; 
they form the " Feutre organique"" (Forel, vol. i. p. 119, Lake of 
Geneva), " Gefilz (Lorenz v. Liburnau in Hallstdttersee^ depth of 
40 m., 1898, p. 189), " Grundalgenzone " (Brand, Starnhergersee, 1896, 
p. 8). Zschokke records that these algas coverings in the high alpine 
lakes are of all the more importance as producers of oxygen, as the 
water above 1800 m., according to Boussingault, only absorbs, as stated 
above, small quantities of oxygen, owing to the diminished atmo- 
spheric pressure. 
The main work on the flora in the alpine lakes of this district 
is Magnin's La vegetation des lacs du Jtira^ 1904. The belts are 
the same as in our lakes : the Scirpiis-Phragmites zone, the Nupliar- 
Potamogeton natans zone, the Potamogetoji lucens-perfoliatus zone, the 
Characea; zone. As specially characteristic of the lakes of Jura, 
Magnin mentions the great development of a Nuphar zone (pp. 374, 
408). He further remarks on a considerable difference between 
the flora in lime districts, specially characterised by many Charace^, 
and in the silicate districts, and maintains that not only the Characese^ 
but also the Potamogeton^ attain their greatest development in high 
mountain lakes, not in the less highly situated lakes. 
Even if the oro^anic life is instrumental in causing the decalcifica- 
tion of the lake-water and the richness in lime of the lake-bottom, it 
is hardly of so great importance here as in the Baltic lakes : in part 
owing to the lower summer temperature, in part because a much 
greater amount of the organic material of the lake is destroyed in the 
lake itself and again acts, through the carbonic acid set free during 
the destruction processes, as lime dissolving. The blue-green algae 
especially (Lake of Geneva, Neuchatelersee, Chodat, 1897, p. 289, 
1898, p. 49; lac d'Annecy, Le Roux, 1907, p. 347) and the Characeas 
seem to play the most prominent part as decalcifiers. 
It must be said that, as a rule, the deposits derived from plankton 
and from the littoral region are not nearly so instrumental in closing 
up the lakes as in the Baltic region. The filling up and the dis- 
