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Original g^rticlcs.
��ON POLYGONUM NODOSUM. By W. T. Thiselton Dyer, B.A., B.Sc ,
Henry Trimen, M.B., F.L.S.
The two species o^ Polygonum, P. Perfticaria, L., and P. lap nthi folium, L., are coiispiciioiisly represented in the late summer vegetation of broken and uncared-for land about London, -by several easily recogin'zed forms. Like the Chenopodiums and Atriplexes that grow with them, they flourish on ground which has been liberally cultivated till laid out for building, but which has not yet become hard and consolidated l)y the alternate action of rain-wash and sun-baking. There are always plenty of spots in the advancing outskirts of the suburbs where these conditions are to b< found, and it is seldom necessary to look far for a place to study Poly' (/OHinns.
Quite the commonest of the London forms, though perhaps not else- where so frequent, are those which are described in English books under the names of P. nodosum or P. laxum. (See Fl. Middlesex, pp. 243, 244.) They are not perhaps collectively separable from typical P. lupaihi folium, by very satisfactory characters, yet they belong to a type which has been well figured by Curtis, Reichenbach, and Babington, and is thoroughly familiar to Metropolitan botanists, — having a certain characteristic fades which serves the ends of recognition, as well perhaps as anything more definite. Typical P. lapatlii folium has a somewhat ditiuse mode of growth, and dense cylindrical and remote racemes, with perianths and unspotted stems of a dull apple-green colour. The P. nodosum, of authors, on the other hand, is rather erect than diffuse, and has stems usually spotted ; racemes collected into a more or less distinct pyramidal panicle, laxer, and narrower in proportion to their length ; the perianths also are reddish and smaller, and the fruit is, roughly speaking, half the size of that of P. lapathifoUum. It was well known to the ante-Linnsean botanists; the Persicaria latifolia geuiculata caulibns maculatis, D. Rand., which was found "passim circa Londinum " (Bay, Syn. iii. 14.5), belongs to it; and two forms were distinguished by Buddie, and are preserved in his herbarium (Herb. Sloane, vol. cxvii. fol. 20). It was described and figured by Curtis under the name of P. Pensylvanicum var. caule maculato (Flor. Lond. f. 1), by Reichenbach as P. nodosum, Pers. (Iconog. Bot. Cent. V. ic. 689), and finally by Babington as P. laxum,^e\c\\. (E. B. S. 28 22). In each case it seems extremely probable that the plant has been wrongly identified. Curtis probably followed Hudson in referring these glandular Polygonums to P. Pensylvanicum,, L., with which, however, they have little coiuiection. It is less easy to decide its claims to be considered the P. nodosum of Persoon. As, however, the description given by that author of his plant is very short, the whole may be quoted for comparison : —
- Nodosum, caule elongato maculato ad geuiculas nodoso, vaginis nudis,
fol. ovato-lanceolatis, spica ramosa. Hab. In humidis, in ruderatis rarius. Caul. 3-pedalis, unc. 1 crassus. Fol. margine et ad petiolos scabra. An a Persicaria specie diversum? (Syn. Plant, vol. i. p. 440.)
VOL. IX. [FEBRUARY 1, 1871.] D
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