Pistiacee. | FLORA OF TASMANIA. ' 37 
Nar. On». V. HYDROCHARIDEZA. 
There are three Australian genera of this Order; one, Damasonium, contains a single species very 
closely allied to, if not identical with, an Egyptian and Indian plant; the second, Hydrilla, consists also of 
one species, which is found throughout the Old World, from East Prussia to South Africa and India; the 
third is the present, a very singular plant, the economy of whose fertilization is one of the most curious in 
the vegetable kingdom. 
: Gen. I. VALLISNERIA, Z. 
Flores dioici. Masc. Spadix brevissime pedunculatus, conicus, spatha trivalvi inclusus, floribus ses- 
silibus minimis undique tectus. Perianthium tripartitum, lobis valvatis. Staminodia 4. Stamina 1-3, 
perianthii laciniis alterna, filamentis brevibus, antheris globosis. Fam. Flos sessilis, spatha tubulosa in- 
clusus, scapum longissimum spiraliter tortum terminans. Perianthium superum, 3-partitum. Staminodia 
3, perigonii laciniis alterna. Stigmata 3, magna, ovalia, sepius bifida, extus quandoque appendiculata. 
Ovarium l-loculare, placentis 3 parietalibus. Bacca cylindrica, perigonii limbo coronata, polysperma. 
Semina cylindriea, ascendentia, testa coriacea, echinata; embryone exalbuminoso, orthotropo, extremitate 
radiculari infera.—Herbe submerse, perennes, stolonifere; foliis linearibus, elongatis, submembranaceis, 
clathratim venosis, apice serrulatis; floribus parvis, masculis fere microscopicis. 
l. Vallisneria spiralis (Linn. Sp. Pl. 1441); foliis linearibus obtusis apice serrulatis.— Br. 
Prodr. 345. 
Has. South Esk River, in deep and shallow water, and probably common elsewhere, Gunn. 
Disrris. Australia, and generally diffused in the warm-temperate and tropical parts of the world. 
Pallisneria spiralis is a submerged fresh-water herb, with fibrous roots, a very short stem, sending off lateral 
. suckers, and very long, flat, linear, green leaves, serrulate at the tips. The male and female flowers are on different 
plants. The male inflorescence (of which I have seen no Tasmanian specimens) is an almost sessile spathe, con- 
taining a small, short Spadix, covered with little globose, sessile, white, almost microscopic flowers; these become 
detached from the spadix, ascend to the surface of the water, expand by three valvate segments, and expose one to 
three minute stamens, alternating with some staminodia. The female flower is solitary at the apex of a very long, 
spirally-twisted filiform peduncle, which, by unrolling its spire, allows the flower to reach the surface of the water, 
and there expand. The female flower consists of a cylindrical ovary, crowned by three small, spreading perianth- 
lobes, has three staminodia, and three large sessile stigmata. The pollen, detached from the floating male flowers, 
fertilizes the female, after which the spiral peduncle again contracts, and the female is carried to the bottom of the 
water, where it ripens its fruit.—Pruit a cylindrical berry, 4-2 inches long, with many ascending, ridged, and 
toothed seeds, attached to parietal placentee. . (Named in honour of Antonio Vallisneri, an Italian botanist.) — 
Nar. On». VI. PISTIACEJE. 
A very small Order, containing a few genera of water-plants, closely allied to Aroidee, of which they 
are no doubt very reduced forms. The tropical Duckweed, Pistia, which abounds in the fresh waters of 
the Old and New Worlds, has not hitherto been found in Australia. 
Gen. I. LEMNA, L. 
Flores hermaphroditi v. abortu dioici, fissura frondis lenticularis cellulose inserti, spatha membra- 
nacea inclusi. Stamina 1-2, exserta; filamentis inzequilongis? antheris didymis. Ovarium sessile, 1-locu- 
lare; ovulis 1-4, basilaribus, stylo brevi; stigmate truncato. Utrieulus membranaceus, 1-4-spermus. 
VOL. EI. 
