WATER PLANTS 



G21S 



WATER POWER 



ana produce one-third of the watermelon crop 

 of the United States, worth annually nearly 

 five million dollars. 



WATER PL ANTS,, or AQUATIC, a kwat'ik, 

 PLANTS, a general name applied to any 

 plants which live either wholly or partly in 

 water. Some of these plants are rooted in the 

 ground and grow through the water, raising 



WATER PLANTS 

 Known also as hydrophytes and aquatic plants. 



their leaves and blossoms above the surface. 

 The leaves of some of these are very large, 

 often attaining a diameter of six feet or more 

 in tropic countries, and the flowers are some- 

 times very beautiful. Other plants remain al- 

 most wholly under water, the leaves in that 

 case becoming small and more or less thread- 

 like, while the flowers are far less showy. 

 Many of the seaweeds and some plants in the 

 inland waters are buoyed up by bladders that 

 form on the leaves, and in a few species the 

 plants break loose entirely from the earth and 

 float about in the waters, from which they 



obtain their nourishment by means of then- 

 roots. 



The water plants differ as much among them- 

 selves as do the land plants, and are found to 

 belong to many families. Some of the best 

 known among them are the beautiful white 

 water lily, common on lakes and ponds; the 

 water hyacinth, which spreads so rapidly that 

 it sometimes blocks the channels of lakes and 

 rivers; and the cat-tail or bulrush, which chil- 

 dren soak in oil, light and use as a torch: 



Related Subjects. The following water plants 

 are given specific treatment in these volumes : 

 Algae Nelumbo 



Bladderwort Papyrus 



Bulrush Rush 



Cat-Tail Seaweed 



Lotus Water Lily 



WATER PO'LO. See POLO. 



WATER POWER. Most of the large fac- 

 tories, mills and electric plants of the world 

 are located on the banks of rapidly-flowing 

 streams, because water power is much less ex- 

 pensive than any other for operating machin- 

 ery. The establishment of the plant, which 

 usually requires the construction of a dam and 

 canals, or conduits, to convey the water to the 

 wheels (see WATER WHEEL), may call for a 

 large investment, but the expense of operation 

 is much less than that of operating a steam 

 plant of equal power. Moreover, many water- 

 power sites have the advantage of furnishing 

 power to several mills from the same dam, 

 through the construction of canals leading from 

 one plant to a second, from the second to a 

 third, and so on down the stream. Plants so 

 constructed are said to be arranged on the cas- 

 cade plan. Excellent examples of this arrange- 

 ment are found in Manchester, N. H.; Lowell 

 and Fall River, Mass.; Rochester, N. Y.; Min- 

 neapolis, Minn., and in many other large manu- 

 facturing centers. 



How Measured. Theoretically, water falling 

 from a higher to a lower level exerts a power 

 equal to the weight of a column of water as 

 high as the distance from one level to the 

 other. To .illustrate: a cubic foot of water 

 weighs 62.5 pounds; therefore a column of 

 water two feet in width, one foot from front 

 to back and ten feet high would weigh 1,250 

 pounds, and at its base it would exert a pres- 

 sure of 1,250 pounds. If this water is allowed 

 to flow against the buckets of a water wheel, it 

 will cause the wheel to revolve with sufficient 

 force to operate light machinery. 



The actual power developed, however, is al- 

 ways less than that theoretically estimated. 



