STRUCTURE AND HISTORY OF PLAV. 261 
аге regarded as pieces of Plav, not as complete Plavs, the former of which is. 
contrary to my opinion. 
Some Plavs are certainly attached—for instance, those forming the con- 
tinuation of the rooted reed-platform of the shallow water round the grinds 
(see p.243)—but Plav also occurs in places where connection with a grind is. 
impossible. In such cases it may be that the Plav is attached, at one side, 
to a shoal under water, ог to the rooted-reed of the adjacent reed-swamp ; ог 
it may be that the Plav, though originally completely unattached, has come: 
to rest on one side owing to subsequent local heaping up of fluvio-lacustrine 
ooze; or possibly, in some cases, the Plav is not attached at all but is 
prevented from moving horizontally because it happens to be almost, or 
completely, surrounded by reed-swamp. If a completely detached Plav 
happened to become liberated where no swamp barrier existed, it would 
drift about freely, and, in fact, be one of Dr. Antipa's “ Schwimmende. 
Inseln." 
Floating-islets are, however, as a rule very much smaller in area than 
Plavs, which possibly indicates some fundamental difference. However in 
Lake Iacob, near Caraorman, I sectioned a floating-islet which was quite as 
large in area as an ordinary Plav. In any case, the round or oval shape of 
these islets (see Pl. 21) appears to me to preclude the possibility of their 
being small pieces of Plav sliced off by ice. If, then, floating-islets are 
not pieces of Plav, Plav and floating-islets are one and the same thing, and, 
in that case, Plav must be described as occurring both fixed and free-floating, 
according to circumstances, and therefore as moving both vertically and 
horizontally. 
The thickness of the aquatic portion of Plav varies. The average thick- 
ness of twenty of the sections I made was 1°34 m. (about 4 feet 4 inches). 
The thickness of Plav, however, ranges from about 2 m. (about 6 feet 
62 inches), in the case of Maximou Kut, a Plav on the north-east side of 
Lake Rosulet, to 0-8 m. (about 2 feet 6 inches), or even less. The same 
Plav also varies in thickness in different places. Thus the Plav on the 
west side of Sherneshenko Sahi *, a small sheet of water off the north-east 
side of Lake Rosulet, is only 0'8 m. (about 2 feet 6 inches) at the edge, 
whereas a few yards further in, it was about 1:45 m. (about 4 feet 9 inches). 
This variation in thickness is probably due to the fact that a Plav grows а 
little at the edge, and thus slightly extends its area. The rhizomes at the 
edge of the Plav loop round and up to the surface (see Pl. 14). That 
there is slight growth there, is also borne out by the fact that the arrange- 
ment of the rhizomes at the edge of a Plav is highly irregular: the rhizomes, 
* The Russian fishermen call the smallest sheets of water Sashka, larger lakes Saha or 
Sahi, and the largest Liman, č. e. lakes like Rosulet, Rosu, ete. In the Norfolk Broads the 
smallest sheets of water are called Pulk-holes. 
