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The Structure and History of Plav: the Floating Fen of the Delta of the Danube.

1916; Linnean Society of London; Volume: 43; Issue: 291 Linguagem: Inglês

10.1111/j.1095-8339.1916.tb00607.x

1945-9483

Marietta Pallis,

Botany and Plant Ecology Studies

Summary. 1 Plav is a floating fen confined in Rumania to the delta of the Danube. It is formed of reed, Phragmites communis, Trin., β. flavescens, Gren. & Godr. 2 Plav is built up almost entirely of vertical reed-rhizomes which, with the aid of their roots, retain much soil. 3 The detachment of the reed, that is the formation of Plav, takes place at a more or less definite stage of growth of the reed. Essential factors to Plav-formation are:— (a)  That the death of the basal rhizomes of the reed coincide with the swamp-stage of its growth; (b)  That the water be deep enough to prevent the reed filling it completely; and (c)  That if there be floods, the amount of silt borne by them be stnall. 4 Change of level of the water or storms are probably almost always necessary to effect final detachment. 5 The reed forming the Plav is probably succeeded by “sedge” (Cladium), or “mixed-sedge” (Carices), and finally by salt-marsh plants. The only competitor with the reed is Typha (2. angurstata, Bory & Chaub., in the delta, and T: angustifolia, Linn., in the Norfolk Broads), but apparently it merely inhibits the growth of the reed for a short time. 6 East-Anglian fen and Plav are fundamentally similar, viz., in structure and in origin. 7 The reed-shoots of Plav vary striliingly in size (in the Norfolk Broads this is also the case, but the variation is less conspicuous). The change in size of the shoots is regarded, in this paper, as a progressive morphological change, senescence which precedes the death of the reed. 8 The reed-shoots are regarded as building up a more or less definite whole—the reed major unit or reed-soma; and the reed-shoots themselves as the minor units or individuals. 9 The major unit is regarded as the total vegetative output which one fertilized cell is capable of initiating, and the minor unit as that portion of the major unit which is able to produce a replica of the specific soma of the major unit. 10 Major and minor individuals are regarded as fundamental units in botany, the former as a constant, its mass as the measure of specific vital energy. The major individual, however, does not necessarily develop its mass in one piece, hence it cannot, in general, be weighed directly. 11 Unlike the major, the minor individual is not a constant, for it varies in size. The variation in size, as already stated, is regarded as morphological and as testifying to the finite duration of the major unit, whose absolute age is thus indicated. In the reed the giant shoots are regarded as the lowest or morphologically juvenile branches of a vast branch-system the first and final branches of which do not co-exist. 12 “Vegetative reproduction” is regarded, in essence, as growth of the major unit or soma, and as taking place through the multiplication of the minor individuals.