Order 1. =Juncaginaceæ.= The ☿, regular, _hypogynous_ flowers have the _perianth_ 3 + 3, _sepaloid_, stamens 3 + 3 (with extrorse anthers), and carpels 3 + 3 (free or united), of which last, however, one whorl may be suppressed (in _Triglochin maritima_ all 6 carpels are developed, in _T. palustris_ the inner whorl is unfertile). Inflorescence long spikes. Embryo _straight_.--Marsh-plants with radical, rush-like leaves, arranged in two rows, and often sheathing and ligulate (“squamulæ intravaginales”); the inflorescence is a spike or raceme.--_Scheuchzeria._ Carpels almost free; in each at least two ovules. Follicles.--_Triglochin_ has long, fine racemes without bracts or bracteoles; one ovule in each carpel. The carpels in the two native species are united, but separate when ripe as a schizocarp, loosening from below; they open along the ventral suture or remain closed; a linear central column remains. ~The most reduced is Lilæa (1–2 sp. Am.)--Protogynous. About 10 species. Temp. Fossils in Tertiary.~ Order 2. =Potamogetonaceæ.= The aquatic plants belonging to this order are perennial, living entirely submerged, or with floating leaves, and preferring still water. The leaves are alternate, in some linear and grass-like, in others there is an elliptical floating blade, supported by a linear submerged petiole. Axillary scales. The fruit is generally a syncarp with _nuts_ or _drupes_; the _embryo is curved_, of very various forms. _Potamogeton_ (Pond-weed). The rhizome is creeping, sympodial (with two internodes in each shoot-generation); the inflorescence is a terminal, many-flowered spike, without floral-leaves; below it are found 2 foliage-leaves placed nearly at the same height, from whose axils the branching is continued cymosely. The flowers are ☿, 4-_merous_, naked, and consist only of 4 _stamens_, with the _connectives, broadly developed_ at the back of the anthers, _resembling a perianth_, and of 4 _free, sessile carpels_. They are common plants in fresh water. ~The spike, during the flowering, is raised above the water. Wind-pollinated and protogynous.--Closely allied is _Ruppia_ (Tassel Pond-weed), in salt or brackish water. The spike has only two naked flowers, each consisting of 2 stamens and 4 carpels. The stalks of the individual carpels are considerably prolonged.--_Zannichellia_ (Horned Pond-weed) is monœcious; the ♀-flower consists of 4 (2–9) carpels, with membranous, bell-shaped perianth; long styles; the ♂-flower has 1 (-2) stamens. _Althenia._~