STRUCTURE AND HISTORY OF PLAV. 289 
SECTION І. 
Phragmites Plav (Phragmites communis, Trin., В. flavescens, Gren, & Godr.). Nazaraou 
Rinok on Lake Rosulet. The section was cut on Sept. 27th, 1913. The thickness of this 
Plav is about 1:55 m. (about 5 feet), and its surface rises about 4 cm. (about 1-5 in.) 
above that of the water. The depth to the sand, as measured from the surface of the Plav 
on Sept. 28th, was about 2°76 m. (about 9 feet). 
This Plav is typical young reed-Plav. It consists of 3 soi layers. (1) A top layer of 
black, apparently highly organic soil, some 15 em. (about 6 inches) in thickness. Poly- 
stichum Thelypteris, Roth, is rooted in this layer; it is practically the sole accompanying 
plant of young wet Play. (See footnote on page 271 and Plate 20.fig. 1.) (2) A layer, about 
0-8 m. (about 2 feet 10 inches) in thickness, of relatively fine soil, partly organic, held by 
the branched roots and the rhizomes of Phragmites; and (3) A layer of relatively coarse soil, 
some 0:6 m, (close on 2 feet) in thickness, with a smaller organic content than (2), also 
held by the roots and rhizomes of Phragmites. The three shades of the diagram indicate 
the soil differences (see page 262). 
The Phragmites forming this Plav was tall-stout. The aerial portion of the shoots 
shown is about 5'15 m. (about 17 feet) in length, measured from the surface of the Plav, aud 
has a total length of about 6:8 m. (about 22 feet). The tallest shoots as a rule spring 
from the very base of the Рау. This is indicated in the diagram by the vertical 
line which continues the aerial portion downwards through the centre of the Plav- 
layer. Тһе inflorescence (the flag of the diagram) measures about 45 cm.x15 сш, 
(18x6 inches). Water-roots as а rule hang from the base of the Plav-layer, as shown in 
the diagram ; they are clean (light-coloured) if the Plav is floating in a considerable depth 
of water. Plate 15 is a photograph of a section cut through Nazaraou Rinok Plav. 
SECTION II. 
Phragmites (Р, communis В. flavescens, Gren. & Godr.) and Typha Plav (T. angustata, 
Bory & Chaub.) This section was cut on September 20th, 1913, through the largest 
island of Lake Rosulet. The thickness of the Plav is 1'6 m. (about 5 feet 3 inches), and 
its surface about 4 ст. (about 14 inches) above that of the water. The depth to the sand, 
measured from the surface of the Plav, was about 2:9 m. (about 9 feet 6 inches) on Sept. 98th, 
1913. This Plav consists of 3 layers; the three layers shown iu the diagram do not, how- 
ever, indicate soil differences, but the different living plant-layers which build up the Play. 
Only 2 sod-layers could be distinguished, as is indicated by the two shades of the diagrams. 
(1) The top layer is black soil with Polystichum Thelypteris, Roth, rooted in it, and 
measures about 8 ст. (about З inches) in thickness. (2) The next layer consists of living 
and dead Typha rhizomes and remains with a few living Phragmites rhizomes interspersed ; 
it is about 45 сш. (18 inches) in thickness, and the soil is dark. (3) This layer consists 
of living and dead Phragmites rhizomes, and is about 1°1 m. (about З feet 8 inches) in 
thickness. The dark-coloured soil is similar in appearance to that of layer (2). This Plav, 
according to measurements, was nearly aground on Sept. 6th—that is, of course, if the 
fluvio-lacustrine ooze overlying the basal sand-bed was of the same thickness on Sept. 6th 
and 98th. The ooze-layer is so loose in texture that it is constantly shifting. 
The Phragmites here was also giant, but its taller shoots were only about 4'5 m. (about 
15 feet) in length, as measured from the surface of the Plav. The exact depth from 
which these shoots arose was not ascertained, hence the dashes in the diagram termi- 
nating in the vertical line ; however, in all probability they arose from the very base of the 
layer. The aerial portions of Typha measure about 2'3 m. (about 7 feet 6 inches), and 
LINN. JOURN.——-BOTANY, VOL. XLIII. X 
