322 BOTANY AND PALAEONTOLOGY 



containing carbonic acid, has the same influence in promoting vegeta- 

 tion. 



Whatever the cause may be, the bottom of the Mammoth Spring, at a 

 depth of four to eight feet, under the clear water of the fountain, is covered 

 with a carpet of moss of a species (Hypnum noterophyllum, Sull. & Lsqx.) 

 which generally, and at other localities, grows on stones washed by only a 

 few inches of running water. These mosses, torn in great bunches from 

 the bottom, rising up to the surface and floating with the current, are 

 stopped by the leaves and stems of large water-plants, to which they 

 remain attached, and by continuous agglomeration of other mosses, or 

 broken pieces of plants, they form on the surface of the water, wherever 

 the current is not too strong, floating carpets of green turf, which become 

 strong enough to sustain the vegetation of a few species of land plants. 

 The species generally found with the mosses composing this floating turf 

 are : the Horned Pond-weed (Zannicliellia palustris, L.) which lives also 

 under deep water, and is uprooted from the bottom ; three species of 

 Duck's meat, small round floating plants, which generally live on the 

 surface of ponds, but which are here in an unparalleled abundance, with 

 broken branches of all the other species which vegetate in the spring. 

 The compactness of the floating carpet is still increased by small mollusca, 

 especially by a small species with soft shell (Phgsa ancillaria, Say.) which 

 lives there in immense numbers, feeding upon the decomposed pieces of 

 broken plants. It is especially these mollusca with the Duck's meat which 

 attract the water fowls, providing them with a delicate, never-failing and 

 abundant food. The constant temperature of the water (60°) favors, appa- 

 rently, the development of animal life, at least for the shells, and is another 

 cause of allurement for the fowls, especially during the winter months.* 



A number of other species of plants worth mentioning live in the 

 Spring, attaching their roots to the bottom, and raising their long stems 

 to the surface. Around the principal very deep and central basin of 

 the fountain there are two species of Pond-weed (Potamogeton natans and 

 P. lucens) with stems at least twelve feet long. "Where the water is 

 swifter-running, and not deeper than four to six feet, species of the Water 

 Milfoil, another Pond-weed {Potamogeton compressus), the Water Persi- 

 caria, the American Brooklime, the Burr-reed, the Water-weed, the Water 

 Starwort (two species) fill the water with the multitude of their long 

 stems and branches. Near the borders, but still in water one foot deep at 

 least, one finds the Marsh Speedwell, the Mint, introduced by the Indians? 

 and growing with great luxuriance, the Spotted Touch-me-not, the Bur- 



* It is a remarkable fact that no fishes are found in the spring above the dam. Is this phe- 

 nomenon caused by the constant temperature of the water, or by the quantity of air or carbonic 

 acid which it evolves ? 



