ad mont. Candelaria (Hoffmann, n. 853, Herb. Ber.).—Frutex, ramuli glabri foliorum limbi 0,12 longi 0,045 lati, petioli 0,008 longi.

P. Venezuelense; foliis breviter petiolatis amplis oblongo-ellipticis apice acuminatis acutis basi subæqualiter obtusiusculis supra glabris subtus ad nervos hirtellis siccis firmulis, centrali nervo ad apicem ducto adalt. nervos utrinque 6 oppositos subadscendentes supremos ad apicem ductos mittente, amento quam folium dimidio breviori, bractea cucullata vertice inflexo peltam simulanti, bracteis rachis ope extenuati inter se junctis et inter flores productis, bacca obpyramidato-tetragona vertice margine extenuato.-In Venezuela inter Agua Blanca et Cumbote, alt. 5000 (Fendler, n. 2572, Herb. Cand.).—Frutex, ramuli glabri, nodi tumidi, foliorum limbi 0,2 longi 0,15 lati, petioli 0,012 longi.

P. Spruceanum; foliis brevissime petiolatis oblongo-lanceolatis obtusiusculis basi æqualiter cuneatis supra subtusque dense pilosis siccis membranaceis, centrali nervo ad apicem ducto nervos ad apicem utrinque 8-10 subadscendentes, mittente, petiolo villoso pedunculo petiolum duplo superanti, bractea cucullata apice inflexa peltam simulanti.—In Peruvia orientali prope Tarapoto (Spruce, n. 4072, Herb. Kew.).—Ramuli villoso-pilosi, nodi tumiduli, foliorum limbi 0,17 longi 0,05 lati, petioli 0,01 longi.

P. aculeatum; foliis breviter petiolatis oblongo-subovato-lanceolatis apice acuminatis subulatisque basi æqualiter acutiusculis obtusiusculisve supra glabris subtus ad nervos sparsissime hirtellis siccis membranaceis centrali nervo ad apicem ducto ad alt. nervos utrinque 4 subadscendentes mittente, pedunculo petiolum superanti, amento quam folium multot. breviori, bractea cucullata apice inflexa peltam margine ciliolat. triangul. fingenti.-(Spruce, n. 2887, Herb. Franc. Herb. indistincta.) -Suffrutex ?, ramuli glabri, nodi vix tumidi, foliorum limbi 0,085 longi 0,025 lati, petioli 0,003-0,005 longi.

P. Panamense; foliis brevissime petiolatis elliptico-lanceolatis apice breviter acuminatis supra glabris subtus ad nervos puberulis siccis subcoriaceis, centrali nervo ad apicem ducto ad apicem fere utrinque nervos 4-5 patulo-adscendentes venasque fortiores mittente, bractea cucullata apice inflexo peltam triangularem margine ciliolatam subfingenti.—In isthmo Panamá prope Chagres (Fendler, n. 270, Herb. Kew.).-Ramuli subglaucescentes, nodi tumidi, foliorum limbi 0,1 longi 0,055 lati, petioli 0,005 longi.

P. pachystachyon; foliis longiuscule petiolatis ovatis vel elliptico

ovatis supra bullatis subtus villosis siccis coriaceis, centrali nervo ad apicem ducto utrinque nervos 5-6 suboppositos versus marginem adscendentes mittente, bractea oblongo-subcucullata sessili utrinque vertice obtuso excepto nudo glanduloso-puberula.-In Columbia (Triana et Linden, n. 162, Herb. Kew.) et Bogotá, alt. 2700 (Triana, n. 52), et Costa Rica (Hoffmann, n. 856, Herb. Reg. Ber.).—-Ramuli appresse puberuli, nodi tumidi, foliorum limbi 0,1-0,12 longi 0,065-0,08 lati, petioli 0,02 longi.

P. inæquale; foliis petiolatis oblongo-lanceatis apice acuminatis. acutis basi inæqualiter rotundatis subcordatis utrinque glabris siccis subcoriaceis, centrali nervo ad apicem ducto ad alt. nervos alternos lat. min. 5 maj. 6 subadscendentes supremos fere ad apicem ductos mittente, bractea cucullata, vertice inflexo peltam margine ciliolatam subsimulanti. In Guyana? (Herb. Rich. in Herb. Francov.).-Frutex, ramuli glabri, nodi tumiduli, foliorum limbi 0,18 longi 0,075 lati, petioli 0,03 longi.

P. cordulatum; foliis petiolatis oblongo-lanceolatis basi subæqualiter cordulatis utrinque glabris siccis rigidis, centrali nervo ad apicem ducto ad apicem utrinque nervos 11-13 alternos mittente, pedunculo quam petiolum breviori, bractea cucullata vertice peltam triangularem simulanti.—In isthmo Panamá prope Chagres (Fendler, n. 267, Herb. Kew.).-Ramuli glabri, nodi haud tumidi, foliorum limbi 0,14 longi 0,0045 lati, petioli 0,02-longi.

P. calceolarium; foliis petiolatis e basi cordata ovato-lanceolatis supra crebre bullatis pilosisque subtus molliter pubescentibus lacunosis siccis membranaceo-coriaceis 5-7-nerviis, centrali nervo ad apicem ducto supra basin nervos utrinque 2 alternos subadscendentes mittente, lateralibus nervis utrinque 2-3 subadscendentibus, petiolo villoso pedunculum villosum superanti, amento mucronato, bractea calceoliformi subtus et margine subvillosa.-In Columbia (Triana et Linden, n. 339, Herb. Kew.).—Rami appresse villosi, nodi tumidi, foliorum limbi 0,07 longi 0,05 lati, petioli 0,015 longi.

a. foliis rameis 0,13 longis 0,06 latis, ramis retrorsum villosis.— In Novæ-Granatæ prov. Antioquia, alt. 1300 (Triana, n. 21, Herb. Cand.).

P. subfuscum; foliis longiuscule petiolatis rotundato-ovatis apice subattenuatis acutis basi subæqualiter profunde cordatis supra parce pilosulis subtus dense fusce pubescentibus siccis rigidulis 9-nerviis,

centrali nervo ad apicem ducto ad alt. nervos utrinque 4 alternos patulo-adscendentes supremos ad apicem ductos mittente, lateralibus nervis utrinque 4, pedunculo petiolum æquanti, amento crasso folium superanti, bracteæ calceoliformis vertice carnosulo margine ciliolato.In Costa Ricæ regione sylvatica ad Alto de la Cruz (Hoffmann, n. 544, Herb. Reg. Ber.).-Frutex vel arbor 6 ped. (Hoffmann, 1. c.), ramuli juniores dense fusce pubescentes, foliorum limbi 0,32 longi 0,24 lati, petioli 0,04 longi.

b. Stigmata 3. Stam. plerumque 6, ovario incomposito raro 3.

P. Victorianum; foliis breviter petiolatis ellipticis vel lato-ovatoellipticis apice acuminatis apice imo obtusiusculis basi subattenuatoacutiusculis supra glabris subtus ad nervos subtiliter hirtellis siccis firmule membranaceis 5-7-nerviis, pedunculo petiolum subsuperanti, amento quam folium breviori, bractea obovato-cucullata apice inflexa, stam. 5, bacca ovato-acuta basi rhachi subimmersa, rhachis foveolis hirtopuberulis.-In Venezuela prope Victoria, alt. 2000 (Fendler, n. 1139, Herb. Cand.).—Frutex, nodi tumidi, foliorum limbi 0,11 longi 0,06 lati, petioli 0,008 longi.

183

P. Lindenianum; foliis brevissime petiolatis elliptico-lanceolatis utrinque acutis utrinque glabris siccis rigidis quintuplinerviis, centralibus nervis 3 paulo supra basin solutis, pedunculo petiolum superanti, amento mat. folium æquanti subremotifloro, rachi subtiliter hirtella, bractea ovato-concava sessili, stam. 3, duo lat. uno postico.-In Cuba prov. Pilos de las Handones (Linden, n. 1177, Herb. Cand.).—Frutex, nodi tumidi, foliorum limbi 0,055 longi 0,025 lati, petioli 0,003 longi.

P. Tiguanum; foliis petiolatis ovato-lanceolatis apice acuminatis acutis basi æqualiter rotundatis truncatisve cordulatisve utrinque glabris siccis membranaceis septemnerviis, nervis 3 centralibus ad apicem ductis, amento folium superanti, bractea obovato-spathulata, stam. 5, bacca ovata olivacea aromatica, stigmat. 4-5.—In insulis Tigu (Barclay, n. 2722, Herb. Brit. Mus.) et Honduras (Barclay, n. 2633, l. c.) et Tamper (Berlandico, Herb. Cand.).—Frutex 3-pedalis, ramuli glabri, nodi tumidi, foliorum limbi 0,085 longi 0,05 lati, petioli 0,02 longi.

c. Stigmata 4.

P. hirtellum; foliis brevissime petiolatis oblongis oblongo-lanceola

tisve apice acuminatis acutis basi rotundatis supra glabris subtus ad nervum centralem subtilissime puberulis siccis membranaceis, centrali nervo ad apicem ducto ad apicem utrinque nervos 8-10 patulo-subadscendentes vel apicem versus venas fortiores mittente, pedunculo petiolum æquanti, amento quam folium triplo breviori sublaxifloro, rachi dense molliter hirtella, bractea breviter pedicellata apice saccato-galeata acuta dorso subtiliter hirtella.-In Brasilia (Sellon, Herb. Reg. Ber. n. 228). Frutex, ramuli glabri, nodi tumidi, foliorum limbi 0,12 longi 0,035 lati, petioli 0,003 longi.

P. Francovilleanum; foliis brevissime petiolatis subovato-ellipticis apice protracto-acuminatis acutis basi inæqualiter rotundatis latere maj. auriculatim producto supra glabris subtus ad nervum centrale villosis margine ciliatis siccis rigidulo-membranaceis, centrali nervo ad apicem ducto ad apicem nervos utrinque 20 alternos venasque fortiores patulo-adscendentes mittente, pedunculo petiolum multot. superanti, amento quam folium triplo breviori densifloro, rachi villosa foveolata, bractea prope florem inserta lanceolata.—In Brasilia prope Barra (Spruce, n. 1784, Herb. Francov.) et San Gabriel da Cocheira ad Rio Negro (Spruce, n. 2362, Herb. Cand.).-Fruticulus simplex apicem versus dense villosus, nodi tumidi, foliorum limbi 0,2 longi 0,085 lati, petioli 0,005 longi.

WOLFFIA ARRHIZA, Wimmer, IN ENGLAND.

BY HENRY TRIMEN, M.B. LOND., F.L.S.

The rivers and ponds of Great Britain will probably well repay an active search by yielding several species of water plants not yet noticed as inhabitants of this country. The Lemnaceous plant forming the subject of this article has been hitherto overlooked in England, though now that attention is drawn to its existence here, it is likely to be found in many places within our boundary.

The locality where I detected this—I suppose our smallest phanerogamous plant-is a pond near Staines, Middlesex. It grows in abundance there, floating on the surface of the water between the fronds of Lemna polyrrhiza, L. gibba, and L. minor.

The genus Wolffia (named after Johann Friedrich Wolff, author of a

'Commentatio de Lemnâ,' Altdorff, 1801) was founded by Horkel on an Egyptian plant to which I shall presently allude, and was first accurately defined by Schleiden in 1839 (Linnæa, vol. xiii. p. 389). In this paper only one species, W. Delilii, is given, but in a reprint of the paper in 1844 (Beiträge zur Botanik, vol. i. p. 233), the author added the Lemna arrhiza of Linnæus to the genus, under the name of W. Michelii. In 1849, Weddell (Ann. des Sc. Nat., 3rd series, vol. xii. p. 170) described another species, W. Brasiliensis.

:

From these papers, and an elaborate memoir on Lemna arrhiza (L.), by Hoffmann, published in 1840, in Weigmann's Archiv., and translated in the Ann. des Sc. Nat., 2nd ser., vol. xiv. p. 223, the following definition of the genus has been derived :WOLFFIA, Horkel and Schleiden.-Horkelia, Rchb.-Flowers monocious, altogether naked. Male flower:-Stamen 1. Filament very short and thick; anther subglobose, unilocular. Female flowerOvary one, 1-celled, 1-seeded. Ovule atropous, nearly erect Style very short. Fruit a spherical, 1-seeded, indehiscent utricle. Seed globose, erect, with a double integument, the outer fleshy, the inner thinner, indurated above, and forming an operculum pervious at the apex. Embryo thick, turbinate, in the axis of the seed, radicle superior.-Flowers arising from a pit in the centre of the upper surface of the frond. Plants increasing chiefly by gemmation, the bud (new frond) single, growing from within the base of the extremity of the parent frond and shortly stalked. Rootless. No spiral vessels.

The plants composing this genus seem to require separation from Lemna on account of their different mode of gemmation, the absence of roots, the central position of the flowers, and the single stamen. The cells composing the epidermis are also of a different shape, being bounded by straight instead of flexuose sides, as in Lemna, the stomata also are larger and the cellular structure of the frond more lax than in the species of the latter genus.

The synonymy of the British species is as follows

:

Lenticularia omnium minima, arrhiza, Micheli, Nov. Plant. Genera, p. 16 (1729).

Lemna arrhiza, Linn. Mant. ii. 294 (1767).

Wolffia Michelii, Schleiden, Beitr. z. Botan. i. p. 233 (1844). "Telmatophace arrhiza," Welwitsch, Herb. Lusitan. (sp. coll. 1848).