Anacharis-(Elodea canadensis). Also called Ditch-Moss, WaterPest, Water-Thyme, Babbingtons-Curse. A fine oxygenator for outdoor pools. Located where there is plenty of sun, it is an extremely free grower, as some of its unflattering names imply. A wild form, somewhat smaller and sparsely foliated, grows throughout the United States and in southern Canada. This, if transplanted to your pool, will do very well, but the cultivated form is inexpensive and far superior. In an aquarium indoors, either form does poorly. A healthy, cultivated plant in an outdoor pool is about 6 inches long, with pliant stems bearing whorls of deep green, willowlike leaves. It spreads quickly by runner and, if it can find enough soil in which to root, will develop a plant chain several feet long on the bottom of the pool. As the plant extends itself, the growth at the older end of the chain becomes yellow. It has to be controlled by pinching off the old growth and keeping only a foot or so of the plant at the new end of the chain.

Cabomba- Also known as Washington Grass, Fanwort, Water-Shield. It probably was a sprig of this plant that the man at the pet store threw in free when you bought goldfish. A good oxygenator, and the fish eat parts of the tender foliage. Other virtues are the lacy appearance of the fanlike leaves and the fact that a piece of any needed size can be pulled from the growing mass and dropped into bowl or aquarium. Cabomba propagates principally by branching. Aquarium sprigs are usually 5 to 6 inches long, but left alone with plenty of room, stems grow several feet in a season.

caroliniana-Grows wild in ponds from Pennsylvania to North Caro-lina, the form usually sold or given away with goldfish.

roseafolia-Similar but with a reddish cast to stems and undersides of leaves.

Ludwigia-Also called Swamp Loosestrife. Basically a marsh grower, but this does quite well as a partially submerged aquatic if planted in shallow water at the edge of a pool where it can break the surface with its upper foliage. It grows from about 6 inches to 2 to 3 feet and bears round, glossy green leaves. It sends roots out horizontally, and new growths spring from them. To keep the plant under control, trim off the new end of the chain. When the old plant exhausts itself, propagate by planting a few cuttings in a 2-inch pot of wet soil with a top layer of sand. Keep the soil saturated. By the time the cuttings rot, they will have produced small new growths, which can then be set out where desired. If allowed to develop in strong sunlight, the leaves will take on a copperish tinge, bright red on the undersides. Grows wild at the edge of streams throughout North America, but the wild form is inferior to a cultivated South American form, which is the variety most dealers have.