501 



catches recorded in the tables, and show in the plates of the 

 plankton of Quiver, Dogfish, and Flag lakes. The sessile or- 

 ganisms above named, with the Bryozoa, which often occur on 

 Ceratophyllum, avail themselves of the plankton as food. Hydra, 

 especially, increases when the plankton is more abundant. In 

 Quiver Lake on May 8, 1896, Hydra was taken in plankton at 

 the rate of over five thousand per m. 3 of water. These organ- 

 isms which find a substratum and shelter on the aquatic veg- 

 etation must have some important effect on the plankton, and 

 their presence is doubtless one of the minor factors in the 

 suppression of the plankton in lakes rich in submerged vege- 

 tation. 



The economic aspects of the question of vegetation in 

 bodies of water arise from the relation which it bears to the 

 production of marketable fish. Quiver and Thompson's lakes 

 are both seined by local fishermen, and their relative produc- 

 tivity as fishing grounds may be expressed in the market value 

 of the leaseholds of the fishing privilege. Quiver Lake is so 

 blocked with vegetation that clearing it for seining is at times 

 an expensive operation, and this has a tendency to lower its 

 market value. Thompson's Lake, on the other hand, is less 

 accessible, and some clearing out of the littoral belt of vege- 

 tation is always necessary before seining, the operating ex- 

 penses being thus somewhat increased. For years the lease- 

 hold of Quiver Lake has been purchased for a merely nominal 

 sum, not exceeding $100, and it has often lacked a purchaser. 

 Thompson's Lake, on the other hand, has been, in recent years at 

 least, an object of increasing value, and brings over ten times 

 this amount for a portion of the lake only. Thompson's Lake 

 has an area of about 1,200 acres, while Quiver has only 230. 

 Their market values are thus out of proportion to their re- 

 spective areas. Capt. J. A. Schulte, of Havana, whose knowl- 

 edge of the fishing industry in the Illinois River is extensive 

 and accurate, estimates that in the same area Thompson's Lake 

 will produce five times as much fish as Quiver, and production 

 of fish thus stands in somewhat the same ratio as the average 



