256 MISS MARIETTA PALLIS ON THE 
The question of senesence is discussed on more general, i. e. biological, 
lines by Minot *, Dastre f, Child }, Metchnikoff $, and many others. Among 
the above publications I am particularly indebted to Professor Benedict’s 
papers and also to the article in the Contemporary Heview : these papers 
were of very great assistance in enabling me to define these problems. 
The Growth Stages. 
There are three more or less well-marked stages of growth of the reed, 
namely, the open and the closed reed-swamps, and, in deep waters, Plav. 
Each of these stages becomes automatically transformed into the stage 
immediately above it, hence the separating line between the stages is not sharp. 
In shallow water, only two stages can be named, not because the develop- 
ment of the reed itself differs in shallow and in deep water, but because the 
closed reed-swamp of shallow water, though similar to Plav in structure, 
never becomes detached, that is to say typical, Рау. This “fixed Plav ” of 
shallow water is sometimes joined to “floating Plav” and it passes into 
2 reed-ledge as the water deepens. In all probability both the ledge and 
the fixed reed-platform into which it passes occasionally become buried under 
inorganic flood-borne sediment as Dr. Antipa has explained (see p. 246). 
When all the stages are present, their order with reference to the open 
water i$: (1) open reed-swamp, (2) closed reed-swamp, and (3) Plav. But 
not all water where there is reed is bordered by open reed-swamp ; closed 
reed-swamp and Plav in some cases abut on the open water directly. 
Open Reed-swamp. 
The open reed-swamp is the stage at which the growth of the reed-shoots 
is as yet sparse. 
Open reed-swamp advances more or less concentrieally, if the spot on 
which it has settled has no irregularities. It advances from the edge of a 
lake and narrows down the central water-space, but it also occasionally 
forms small independent circular or oval patehes away from the marginal 
reed-swainp. These reed-patches have apparently arisen from seed, or 
possibly, though improbably, from detached pieces of rhizome (see p. 250). 
I saw several such patches in Lake Merhei, in the northern portion of 
the delta. They were only a few feet in diameter, and probably not more 
than two or three years old, as the reed-shoots only rose some 0*6 m. (about 
2 feet) above the surface of the water, and none of the shoots bore 
flower. In Lake Lumina I saw several much larger patches consisting of 
* Minot, C. S., “The Problem of Age, Growth, and Death,’ New York, 1908; and 
“Problems of Modern Biology,” Philadelphia, 1913. 
t Dastre, A., “Га Vie et la Mort." Paris, 1918. 
f Child, C. M., “Senescence and Rejuvenescence.” University of Chicago Press, 1915. 
$ Metchnikoff, Élie, * The Nature of Man," 1903; and * The Prolongation of Life," 1908. 
