We have pond-weeds in abundance, but the Potamogetons are the pond-weeds par excellence. There is scarcely a piece of water in this country, be it river, lake, pond, canal, or intermittently dry ditch, but has one or more species growing there. The genus is a very difficult one, such as it is impossible to do more than show the general characters of here. Hooker and Bennett, in their revision of the genus, give twenty-one British species with a number of connecting sub-species and varieties. The one figured here is the Oblong Pond-weed (P. polygonifolius), with narrowly egg-shaped floating leaves, and narrower submerged leaves. All have long leaf-stalks. The floating leaves always present the upper side to the air, and are always perfectly dry. The flowers are greenish and unattractive, collected into a slender spike. Individually they consist of a four-parted perianth, four stamens, four carpels. There is a species (P. natans) with broader floating leaves and narrow submerged leaves. A broader still is P. plantagineus, with clearer leaves and more slender leaf-stalks. P. crispus, P. densus, P. perfoliatus, P. prÆlongus, etc., have only submerged leaves, which are more or less oblong.

The species with floating leaves form refuges for many interesting low forms of life, and the microscopist will find them very fruitful in specimens for him.

The name is from the Greek words, potamos, a river, and geiton, a neighbour.