Nos. 618-619] RESTOCKING INLAND WATERS 331 



seems applicable is that the water became too warm for 

 them. During these same days, hydra were coming into 

 the hatchery troughs at Saranac Inn and reproducing in 

 such abundance that it was necessary to clean out the 

 troughs every three days. 



In these hatchery troughs, they grow so thick that a 

 perfect mat is formed, covering the bottom and sides in 

 patches two or three feet long. In the center of these 

 patches, the hydras become brown, and, if left for about a 

 week, may become nearly white. They look as if they 

 were dead, but when touched, contract. Hydra taken -in 

 late September in Lake Clear were all brown, with a few 

 that were nearly white. This wide range in color is ap- 

 parently due to metabolic changes taking place in the 

 chloroplastic corpuscles. 



The red hydra are a source of food for fish, for the trout 

 in the hatchery troughs eat them after they become a few 

 weeks old. On first hatching, the small trout are killed 

 by these hydra. After trout fry have eaten freely of 

 red hydra, their droppings are colored red, indicating 

 that the chloroplasts are not broken up in digestion. 

 Doubtless the young fish in the lake and small minnows 

 that secure their food from the stems of plants eat many 

 of these hydra. 



A further question arises in the relation of the fish to 

 the several physiographic conditions in the lake. This is 

 determined by classifying the fish habitats. These are 

 stream, barren sandy-shoal, barren stony-shoal, vegeta- 

 tive and deep-water. 



There is no vegetation growing in the brooks except 

 inside the bridge of Trout Brook where Potamogeton 

 robbinsii and some filamentous algae are found. At the 

 mouth of Meadow Brook a few bullrushes and pond lilies 

 are seen; while the Divide Brook meanders over organic 

 debris in which a few scattering plants of P. robbinsii, 

 succeed in growing. There is a narrow fringe of yellow 

 pond lilies about twenty feet from the mouth of this latter 

 brook, and between the shore and this fringe of lilies a 



