STRUCTURE AND HISTORY OF PLAV. 249 
accident of its aerial existence that has caused it to remain simple and annual, 
instead of its being branched and perennial like the rhizome. Some observa- 
tions were made in 1859 by Reissek* on the development which takes place in 
immersed portions of the aerial stem of the reed ; and he points out that an 
immersed reed-stem, if buried by sediment, is able, to some extent, to fulfil 
the office of a rhizome as regards the acquiring of fresh territory. These 
immersed aerial shoots he calls “ Legehalme." 
Reissek states in his paper that Legehalme can arise anywhere under 
aquatic conditions, but that they do so more readily if the bottom slopes 
and is pebbly, if the situation is exposed, and if the aerial portions of the reeds 
are weak and isolated, and the rhizomes shallow-rooted. Under the above 
circumstances the aerial portions of the reed-shoots bend over, as neither their 
structure nor their surroundings give them support, and sooner or later they 
are blown on to the surface of the water. These blown-over shoots, he goes 
on to remark, grow astonishingly fast in the water, especially if young, 
and often produce internodes 0:32 m. (about 1 foot) or more in length 1. 
Gradually the Legehalme sink and attach themselves to the bottom by their 
roots. A temporary fall of the water favours rooting, because the Legehalme 
are carried down with it, and wherever a node touches the bottom, roots are 
produced. Pebble-banks situated at the edge of stagnant pools, and exposed 
by the falling of the water, are often in the autumn surrounded by 
Legehalme about 14 to about 16 m. (about 47 to 53 feet) in length. Their 
growth in length, Reissek remarks, is unquestionably aided by the slight 
development of the leaves, and they are of some, though slight, use as. 
regards the horizontal advance of the reed under the conditions prevailing 
on the Danube near Vienna, where he worked. 
In the delta of the Danube I also found Legehalme, though they were 
rare, but they were produced under circumstances which differed from 
those described by Reissek. The delta Legehalme did not arise from weak 
isolated blown-over shoots, but from shoots partially, or entirely, severed, 
owing to breakage by fishermen's boats ; also, steep slopes and pebbly 
reaches do not exist in the delta, nor is there a sufficient annual deposit 
of sediment to bury them should they sink. Moreover the water is 
aerial extremity of the shoots is broken quite close to the surface of the water, in which 
case the reed may become tufted near its broken apex. The larva of a small moth, whose 
empty pupa I found in the top joints of the reed, is often responsible for injuries to the 
aerial portions of the shoot. On one Plav, close to Lake Iacob, near Caraorman, a con- 
siderable proportion of the reed-shoots were injured in this way and had therefore one 
or two branches about 12 em. (about 5 inches) in length near their injured apices. 
* Reissek, S., in Verhandl. k.-k. zool.-bot. Ges. Wien, ix. (1859) pp. 55-74. 
t The measurements are given by Reissek in Wiener Fuss. One Wiener Fuss = 
0:31726 metre (a little over one English foot). 
LINN. JOURN.—BOTANY, VOL. XLIII. 8 
