291 



CCLX. PISTIACE^. The Duckweed Tribe. 



PiSTiACEiT,, Rich, in Ilumb. et Bonpl. JV. G. et Sp. 1. 81. (1815) ; Lindl. in TJooker's Ft. 

 ^co^ 2. 191. (1821); Synops. 251. (1829). — Lemnace^e, Dec. and Duhy, 632. 

 (1828.) 



Diagnosis. Floating monocotyledons, with solitary naked spathaceous 

 flowers, and the stem and leaves confounded. 

 Anomalies- 

 Essential Chahacter Floivers 2, naked, enclosed in a spatha. Male: Stamens 



definite. Female: Ovarium 1 -celled, with 1 or more erect ovules; style short; stigma 

 simple. Fruit membranous or capsular, not opening, 1- or more-seeded. Seeds with a 

 fungous testa, and a thickened indurated foramen ; embryo either in the axis of fleshy 

 albumen, and having a lateral cleft for the emission of the plumule, or at the apex of the 

 nucleus. Floating plants, with very cellular, lenticular, or lobed stems and leaves con- 

 founded. Flowers appearing from the margin of the stems. 



Affinities. These are plants of a still simpler organisation than Flu- 

 viales, like them apparently destitute of spiral vessels, and not producing 

 any separate stem or leaves, but a body formed out of both, from within the 

 substance of which proceeds a membranous spathe containing one naked 

 male and one naked female flower; a stem and two flowers thus constituting 

 the whole of the plant. But if an abstraction be made of the simplicity of this 

 structure, and the organisation be considered as if it belonged to plants of a 

 more highly developed character, it will be found that these are really no- 

 thing but Aroidece, the spadix of which is reduced to two flowers of different 

 sexes. But while the accuracy of this view of the nature of Pistiacese is not 

 likely to be questioned, it must be borne in mind that this very reduction of 

 parts is inconsistent with the notion of Aroidese, properly so called; and 

 hence the necessity of constituting a particular order. I find from an ex- 

 amination of seeds of Pistia, most kindly procured from India for me by 

 Dr. Wallich, that the embryo is a minute body lying at the apex of the 

 albumen ; in Lemna it occupies the axis ; in both there is a fungous testa, 

 with a remarkable induration of the foramen of the secundine. The embryo 

 of Pistia is very minute, and perhaps solid ; but in Lemna there is the slit on 

 one side for the emission of the plumula, just as in Aroideee. In Dr. Hooker's 

 Botanical Miscellany , part 2, is an account of the germination of Lemna, 

 by Mr. Wilson of Warrington, which is worth consulting. Agardh refers 

 Lemna to Urticege, and places Nepenthes here. 



Geography. Lemna inhabits the ditches of the cooler parts of the 

 world ; Pistia the tropics. 



Properties. Pistia Stratiotes grows in water-tanks in Jamaica, where, 

 according to P. Browne, it is acrid, and in hot dry weather impregnates the 

 water with its particles to such a degree as to give rise to the bloody flux. 

 Hist, of Jam. 330. A decoction of the same plant is considered by the 

 Hindoostanees as cooling and demulcent, and they prescribe it in cases of 

 dysuria. The leaves are also made into a poultice for the piles. Ainslie. 



Examples. Pistia, Lemna. 



