It is very difficult to decide upon the limits of species in this genus, which, like most aquatic plants, is sufficiently Protean. My own specimens are ban-en, but those of Dr. Gillies and Bridges, from the Andes and west coast of South America, are in flower and monoecious, and from them I have described the ripe carpels. Gaudichaud distinguishes M. elatinoides from M. ternatum, by the former being dioecious ; but D'Urville, in re-describing it, asserts the contrary.
In its normal state, the upper leaves of the present species are much broader than those of any other; but at times, the whole foliage is uniformly capillaceo-multifid, when it can hardly be discriminated from some forms of the European M. vertkillatum.
2. HIPPUEIS, L.
1. Hippuius vulgaris, Linn. Sp. PI. 3. Engl. Bot. t. 763.
Hab. Strait of Magalhaens ; Port Famine, Capt. King.
These specimens, which are barren, do not seem to differ from others of European growth. Both Capt. King's and ]Ir. Anderson's collections contain the plant, so that although the above be the only reported station for it in the southern hemisphere, I have no reason to doubt its authenticity. The range of Hippuris vulgaris, in the temperate latitudes of the northern parts of the world, is very wide, extending from the arctic regions of Europe and Asia (Lapland 70°, Iceland 65°, Siberia and Kamschatka), south to Montpellier, lat. 43° in western Europe; probably reaching 50° in the central', and the Caucasus, or 44° in the east parts of our continent. The late Dr. Griffith collected it in Afghanistan, lat. 32°, its only known habitat in Central Asia. In North America this species is equally diffused, from the latitudes of 55° and 70° on the west coast, and from New York, 41°, to Labrador and Greenland, lat. 70°, on the east. From the interior I have only seen specimens, gathered by Dr. Richardson near Hudson's Bay, between 55° and 60°.
Hippuris is very closely allied to Myriopliyllum, and differs chiefly in the reduction of the four carpels to a solitary one, with an accompanying solitary stamen, placed on one side of the carpel, within the obsolete margin of the calyx.
3. CALLITRICHE, L.
1. Calliteiche verna, L., rid. Fl. Antarct. parti, p. 11. Antliapla, W. Anderson in Bill. Banks.
Var. 0, terrestris ; El. Antarct. 1. c.
Hab. Fuegia, the Falkland Islands, and Kerguelen's Land, abundant ; Anderson (in Cook's 3rd Voyage), /. I). H. Var. /3, Hermite Island and the Falkland Islands.
Callitriche differs from the typical genera of the Order Ilaloragece in having generally caducous bracts at the base of the flowers, in its 4-carpellary ovarium with only two styles, in the entire absence of a limb to the calyx, of a corolla in the female, or of any perianth whatever in the male flower. The latter are truly achlamydeous, but not the former, the calyx being equally obsolete in the carpels of MyriophyUum and in the present genus ; whilst the general symmetry of the parts, the structure of the seed and embryo, of the recurved styles, covered uniformly with stigmatic papillae, and the form of the pollen, are alike in both, indicating a very close natural affinity. In the first part of this work, I alluded to the real form of the anthers in the southern specimens of C. verna, as not differing from the ordinary structure of that organ in Phaenogamic plants, even in appearance, before their dehiscence, and only presenting the hippocrepiform suture on the curling up of the valves, and the union of the two loculi and their lines of dehiscence above.
Callitriche verna is universally diffused throughout the temperate regions of both hemispheres, even entering
