AQUATIC PLANTS IN POND CULTURE. 17 



plants essential in pond culture, but suggested that ponds be con- 

 structed with sand and gravel bottoms with the view to keeping 

 them free of all aquatic vegetation, except in selected places where 

 the plants were to be walled in with concrete, the walled-in portions 

 to be filled in with earth of the richness required by the plants 

 selected. 



At the Mill Creek station of the Michigan Fish Commission for 

 the propagation of both large-mouthed and small-mouthed black 

 bass Chara is the principal plant, and it is quite satisfactory to the 

 superintendent as a food producer. At one time, he asserts " the 

 Potamogeton drove Chara out and I could not raise 100 fish where 

 before the Chara went I could raise 1,000." ^ 



RESUME OF OBSERVATIONS. 



The various estimates of the commoner plants as found at the 

 different stations, together with the differences in condition and 

 environment, make generalization difficult. The foregoing observa- 

 tions seem to show, however, first of all that the fish-cultural value of 

 a species is chiefly a matter of the growth it attains. Its merits as 

 food producer, shelter, and oxygenator are determined by the kind 

 and quantity of its foliage, stems, and roots, and so likewise are its 

 demerits, few plants being objectionable in themselves for any rea- 

 son other than growth that is overabundant or overpersistent. 



The growth of plants, however, being a matter of en\dronment, 

 depends chiefly, in the case of rooted species, upon the character of 

 the bottom soil. Species most desirable in one locality may be 

 obnoxious in another where by reason of the fertile soil the growth 

 becomes dense and difficult to control. In his paper entitled " The 

 biological relation of aquatic plants to the substratum " Dr. Raymond 

 H. Pond * shows by experiment that VaUisneria spiralis, Ranunculus 

 aquafilis tricophyllus, Elodea canadensis, Mynofhylluin spicatum,, 

 Potamogeton ohtusijoUvs, and P. perfoliatus, hence probably all 

 rooted aquatics, are for optimum growth dependent upon their rooting 

 in the substratum, and his conclusions are abundantly confirmed by 

 observations in the ponds here described. It would seem, however, 

 that his application of the fact to fish culture might be put differ- 

 ently. Although it is true that good soil is to be sought, it should be 

 added that for very rich soil it is important to avoid, if possible, 

 plants with a tendency to rankness. 



The quality of the water is a factor that may entirely control the 

 conditions of fish culture. At Cold Springs, Ga., where the water 

 is soft, it is impossible to obtain a permanent growth of vegetation, 

 and the ponds must accordingly be restocked from time to time. 

 Two species of Myriophyllum are the only plants that have been 

 successfully maintained through a season. It sometimes happens 

 also that even with exuberant vegetation there is a dearth of animal 

 life, and this might be ascribed to some property or deficiency of the 

 water, just as is the abundance of certain amphipods and other crus- 

 taceans that are an important food for young fish, these forms being 

 known to thrive and multiply best in water containing lime. 



» Dwiffht Lydell in Transactions of the American Fisheries Society for 1905, p. 193. 

 * Report U. S. Fish Commission 1903 (1905), pp. 483-526. 



