62 
THE BREAKING OF THE SHROPSHIRE MERES. 
respective species, is the sudden change of their specific gravity, 
which causes them to rise suddenly from the bottom of the water, 
where they are developed in vast numbers, to the surface, and as 
suddenly to sink down again. Such a change of specific gravity 
takes place periodically in higher aquatic plants. The terminal 
buds of Hydrocharis, Stratiotes, Ceratophyllum, Aldrovanda, and 
Utricular ia fall off in the autumn, and sink to the bottom of the 
water, where, protected from frost, they lie during the winter, and 
in the spring rise again to the surface, where they develop their 
leaves. I owe the following interesting description to the kindness 
of a former pupil of mine, Dr. Augustus Schmidt, of Lauenberg, in 
Pomerania. This town is situated near the Prussian frontier, on 
the River Leba, which flows from the adjacent mountainous district 
of Karthaus. After leaving the mountains near the station, Gross- 
Borclipol, it enters the moorland, which extends over many square 
miles; it flows through this moor rather rapidly, but in endless 
windings, and is discharged into the Baltic about four miles to the 
north of Lauenberg. The moor is inaccessible the greater part of 
the year, and can only be traversed in midsummer. The Leba is a 
true moor river ; its banks are quite flat, the bed is nothing but 
moor and swamp which gives way under one’s feet. Whenever the 
river is about two feet deep, the water takes a brown colour, which 
prevents people seeing to the bottom. In July 19th, 1877, the 
river appeared quite green from a vast quantity of minute spherical 
bodies which floated on its surface, and even ordinary people were 
struck by it. The phenomenon, which was first noticed towards 
noon, lasted for about five hours, and had totally disappeared in the 
evening. The next morning there was nothing to be seen ; but at 
noon there was again a large quantity, whilst there were very few 
towards night. It was similar on the third day, but since then the 
minute spherical bodies have entirely disappeared from the Leba.” 
An instance of “ breaking ” has been described by Professor Gobi, 
of the University of St. Petersburg, which he observed on the south 
side of the Gulf of Finland, in 1877, produced by an alga which he 
regarded as identical with Rivularia fiuitans , Cohn, which name he 
proposed to change to Rivularia flos-aquce ; but which MM. Ed. 
Bornet and Ch. Flahault, after examining specimens sent to them, 
Marcit, 1893. 
