Monocotyledons with Petaloid Flowers — Lemnacece . 
ii5 
ROOTS consisting of simple fibres from the under surface of the frond, each sheathed at the extremity by a 
conspicuous sheath ( coleorrhiza ). 
FLOWERS very minute, rarely seen excepting in Lemna minor: L. polyrrhiza, with tufted root fibrils, has not 
been observed in flower in Britain. 
USES, &c.—The Order is of no economic importance. Its chief interest consists in the remarkably reduced 
character of its vegetative system. 
Nattiral Order 
NAIADET 
Diagnosis.— Aquatic marine or freshwater herbs, with floating or sub¬ 
merged stipulate leaves. Flowers small, perfect or unisexual. Perianth of 
4 minute segments or wanting. Stamens 1-4. Pistil apocarpous, of 1-4 
carpels. Seed exalbuminous. 
Distribution. —A small Natural Order, but, as is usually the case with aquatic groups, widely 
dispersed over the Globe. Most of the species of Pondweed ( Potamogetoti ) are found in fresh water, 
but a few species of this genus, and all the other British genera, occur in brackish or salt water. 
Number of British Genera, 5; Species, 18. 
Leaves various : when floating, as in some of the Pondweeds (P. natans and allies), usually elliptical or oblong; 
when submerged, with few exceptions, narrow, linear, or even capillary ; very rarely opposite as in P. densus: in 
Grasswrack (Zostera marina) rooting in sand near low water-mark, narrow-linear from a few inches to several feet in 
length. 
