478 CV. naiadacEjE. [ Potamogeton . 
above, hemispherical beneath, roots solitary. E. B. t. 1233. 
Telmatopbace Schleid. 
Stagnant water, but not very frequent. Rare in Scotland. ©. 
6 — 9. — Size of L. minor, but readily distinguished by its gibbous or 
even hemispherical lower surface, which is, moreover, white, pellucid, 
and beautifully cellular, upper side plane, green, opaque. Stamens 2. 
Ovary with 2 — 7 erect ovules. Utricle at length bursting transversely. 
Seeds usually 2 — 4, rarely more, or solitary, erect. 
Okd. CY. NAIAD ACEiE Juss. 
Flowers perfect 1 and all sessile, or imperfect and monoecious 
or dioecious. Perianth ? of the perfect fl. of 3 — 4 wedge- 
shaped or unguicula.te scales, or wanting ; of the imperfect ones 
usually wanting, sometimes of 1—2 scales. Stamens definite, 
hypogynous. Anthers 1 — 2-celled. Ovaries solitary or several, 
1- celled. Ovules usually solitary, erect or pendulous, rarely 3 
and erect. Style simple, or more or less deeply 2 — 3-cleft. 
Pericarps dry, indehiscent, 1 -celled, 1- (or rarely 2-) seeded. 
Embryo without albumen, with a thin skin, having a lateral cleft 
for the emission of the plumule , straight or curved. Radicle 
large. Submerged or floating aquatics, with very cellular leaves 
and stems. Flowers inconspicuous, sometimes spiked. 
1. Potamogeton. Flowers perfect. Perianth of 4 unguiculate sepals 
Stamens 4. Anthers subsessile. Carpels 4, sessile. Stigma nearly 
sessile, entire. 
2. Ruppia. Flowers perfect. Perianth 0. Stamens 4. Anthers sessile. 
Carpels 4, on long stalks. Stigma sessile, entire. 
3. Zannichellla. Flowers imperfect, axillary. Stamen 1. Anther 
on an elongated filament. Carpels 4 or more, sessile or on a 
stalk not longer than the achene. Style evident, entire. Stigma 
discoid. 
4. Naias. Flowers imperfect, axillary, solitary. Carpels, solitary, sessile. 
Style with 2 — 4 elongated stigmas. 
5. Zoste'ra. Flowers imperfect, arranged on a flat spadix within a 
foliaceous spatha. Carpels sessile. Style with 2 elongated stigmas. 
* Pollen globose or oblong. Plants growing in fresh water , 
rarely in salt marshes. (Gen. 1 — 4.) 
1. Potamogeton Linn. Pond-weed. 
Flowers perfect, sessile, upon a spike (or spadix ?) which 
issues from a sheathing bractea (or spatha ?). Perianth single, of 
1 Dr. Lindley limits this Order to those genera which have imperfect flowers, and 
removes Ruppia , Potamogeton , Aponogcton , and Ouviranda to the Juncaginacca. 
According, however, to the views of Decaisne, Kunth, and some others, the sup- 
posed sepals of these genera are merely bracteas, each stamen and carpel being a 
distinct flower ; so that these plants have really all imperfect flowers, and are 
properly placed here. The perianth, if such it be, is sessile, on a kind of spadix or 
thickish peduncle : in the true Juncaginaccce the lower flowers at least are stalked, 
thus obviating the ambiguity about the perianth or their being truly perfect. 
