A III erica )i Fisheries Society. 89 



THE ROLE OF THE LARGER AC^UATIC PLANTS IN 

 THE BIOLOGY OF FRESH WATER. 



BY RAYMOND H. POND, PH. D. 



The primary object of an investigation of the biology of our 

 Great Ijakes, is to ascertain the factors which determine the 

 quantity of food fish produced. The problems at once JDvohcd in 

 sucli an undertaking are numerous, but may be in a general way, 

 assigned to three groups. In the first group we may include 

 those arising from the various relations which the different ani- 

 mals sustain to each other, such as, food and feeder, enemy and 

 friend, host and parasite, and the like, all of which are sli-idly 

 animal problems to be solved by the Zoologist. In ;i second 

 group, woidd occur such questions as are suggested l^y the rehi- 

 tions existing between aninuils and plants, and to these, the 

 botanists as well as the zoologists may properly give attention. 

 In the third grouj), we could inchule inquiries concerning tlie 

 relation of plants to the soil and water, aud such as belong more 

 especially to the plant physiologist. Such a gTouping of the 

 secondary problems is purely arbitrary, being given to indicate 

 the scope of the investigation, and to lead up to tlie statenu'ut 

 already emphasized by Eeighard and Ward, that a knowledge oi\ 

 the sources of nutrition of our food fishes, involves by necessity, 

 an exhaustive study of the cycle of matter in the lakes. 



There are two ultimate sources of food for the fish, nanudy; 

 soil and air. l^either the fish, nor the animals upon which they 

 feed, can secure nourislnuent from these sources directly. Plants 

 must intervene to organize the mineral salts and carbon dioxide 

 into food for the animals. In the case of the plant plankton, we 

 have a large amount of organic matter that nuiy be considered -Af 

 food available for animals, which themselves in turn are either 

 directly or indrectly used as food by the fish. Thus there occurs 

 in the lake, a manufacturing of mineral salts and carbon dioxide 

 into ])lant ])lankton. and also, a nianuraeturing of plant plank- 

 ton indirectly into fish. It is thus evident, that each season's 

 catch of fish means a witlulrawal of so much organic nuitter from 



