2GS PISTIACEiE. [Zannichtllia. 



linear-setaceous, with sheaths sometimes narrow and small, at other 

 times large and inflated. Spadix at first very short, included in the 

 sheaths or spatha, with two green flowers, one above another on op- 

 posite sides, and quite destitute of perianth. Anthers large, sessile, 

 subquadrate, bursting horizontally, 1 -celled. Mertens and Koch say 

 that each pair is in tact the two cells of one anther, and that there are 

 in reality but two sessile stamens. Pollen, a tube with three globules, 

 one in the middle and one at each end of the tube. Germens re- 

 sembling four minute tubercles in the centre between the anthers. 

 After flowering, the spadix lengthens remarkably, to the height of five 

 or six inches or more, and becomes spirally twisted, as if to bring the 

 fruit to the level of the water, in which the flowers are always im- 

 mersed, but Mr. Wilson observes the fruit to be submerged in every 

 stage. The germens now swell, and their base is elongated into a 

 footstalk, as the fruit ripens, one or two inches long. Each then be- 

 comes an oblique, ovate, acuminated drupe. This drupe is sometimes 

 more beaked than at other times, and the sheaths of the leaves are 

 sometimes but little inflated ; then the plant becomes 7?. rostellata of 

 Koch, and of Reichenbach in his Iconoy. t. 174./. 306." Hookei. 



4. Zannichellia. Linn. Horned-Pond-weed. 



Barren ft. Perianth none. Fertile Jl. Perianth single, of 

 one leaf. Germens four or more. Style one. Stigma pel- 

 tate. Capsules nearly sessile. — Named in honour of John 

 Jerome Zannichelli, a Venetian apothecary and botanist. 



Monozcia. Monandria. 



1. Z. palustris, Linn. Common Horned- Pond-weed. Anthers 

 4-celled ; stigmas entire ; pericarps toothed on the back. J5r, 

 Fl. 1. p. 385. E. Fl. v. iv.;j. 70. E. Bot. t. 1844. 



Ditches and stagnant waters, frequent. Fl. Aug. ©. — Floating. 

 Stems long, filiform, branched. Leaves opposite, linear, entire, some- 

 times emarginate at the point. Flowers axillary, from a membrana- 

 ceous bractea. Fertile fl. upon a very short stalk, from the base of 

 which arises a single naked anther , borne on a short white filament. 



Ord. 76. PISTIACEiE. Rich. Pistia Family. 



Flowers two, naked, enclosed in a spatha. — Sterile Fl. 

 Stamens definite. Fertile Fl. Ovary 1-celled, with one or 

 more erect ovules: style short: stigma simple. Fruit mem- 

 branaceous or capsular, not opening, one- or many-seeded. 

 Seeds with a fungous testa, and a thickened indurated foramen. 

 Embryo either in the axis of a fleshy albumen, and having a 

 lateral cleft for the emission of the plumule, or at the apex of 

 the nucleus. — Aquatic floating plants, with very cellular lobed 

 fronds, which bear the flowers from the margins. 



