But let the taste become bad and the odor repulsive, and a scare is easily started. "There must be dead things in the water, or it wouldn't taste so horrible," is the common verdict. Some newspaper seizes upon the trouble and makes of it a sensation. The ubiquitous reporter writes of one of "the animals" that it "looks like a wagon wheel and tastes like a fish." With such a remarkable organism contaminating one's drink no wonder there is fear of some dread disease. The water is believed to be full of "germs"; whereas the pollution is entirely due to the presence of algae--never poisonous to mankind, in some cases acting as purifying agents, but at certain seasons of the year imparting a taste and odor to the water that cannot be tolerated. Algae--what are they? They are aquatic plants. Algae are not to be confounded with the water vegetation common to the eye and passing by the term weeds. Such plants include eelgrass, pickerel weed, water plantain, and "duckmeat"--all of which have roots and produce flowers. This vegetation does not lend a bad odor or taste to the water. In itself it is harmless, although it sometimes affords a refuge for organisms of a virulent type. But when the aquatic vegetation of the flowering variety is eliminated from consideration, there still remains a group of water plants called algae. They comprise one-fifth of the known flowerless plants. They are the ancestors of the entire vegetable kingdom. Those whose habitat is the sea number the largest plants known in nature. Certain forms found in the Pacific are supposed to be 800 feet in length; others are reported to be 1,500 feet long. The marine variety are familiar as the brown kelps and the wracks, which are very common along our Northern coast. _Plants Which Pollute Drinking Water_ The fresh-water algae are usually grass green in color. This green variety is often seen as a spongy coating to the surface of stagnant pools, which goes by the name of "frog spawn" or "pond scum." One of this description, _Spirogyra_, has done thousands of dollars' worth of damage by smothering the life out of young water-cress plants in artificial beds constructed for winter propagation. When the cress is cut the plants are necessarily left in a weakened condition, and the algae form a thick mat over the surface of the water, thus preventing the growth of the cress plants and oftentimes killing them. The absolute necessity of exterminating these algae led to the perfection of the copper-purification process.