19: 



NATUR.VL HISTORY OF THE FARM 



and sparkling, of a \o\y and constant temperature, "VNith a low 

 oxygen content, and, owing to prolonged contact wnth the 

 soil, with a high niincral content that varies much according 

 to the character of the soil traversed. Deposits of sul]:)hur 

 and of iron are often fonncd about the mouths of mineral 

 s]M-ings. But where the ordinary spring bubbles up, one 

 usually sees only miniature deltas of clean-washed sand at the 

 bottom of a lim^^id pool, which clears itself quickly after 

 roiling. 



Spring water has a population of its own. 

 Man and bird and beast are transient 

 visitors who only quaff its waters; but 

 there are other creatures, that pennanently 

 dwell in them. They are things that cannot 

 endure too great heat in summer or freezing 

 in winter: things that like low equable 

 temperature and partial shade. The most 

 characteristic plant that grows in spring 

 water is water cress (fig. 74) ; it was used 

 by the pioneer to garnish his meat platter, 

 and it is still so used. There are water- 

 mosses, also suited to such a habitat, and 

 many lesser alga3 of various kinds, both 

 green and bro^^^l. 



There are animals, also, that live in 

 spring water; such are the salaniander shown in figure 75, 

 and the brook trout, which does its best in water not warmer 

 than 60° F., and. many other lesser creatures. Most of 

 the great groups of animals are represented there, if 

 by only a few fonns: crustaceans; by the scuds, clamb- 

 ering over and feeding ui)on the water-cress, and by 

 a=;ellus, wallowing in the soft bottom of the pools 

 (fig. 20); molluscs, by little white clams (half an inch 

 long, more or less), of the genus Sphcsrium, furrowing tlie 



Fig. 74. A leaf of 

 watercress. 



