POTAMOGETONS IN RELATION TO POND CULTURE. 283 



ness and precision of a leaf- cutter bee (fig. 74), though usually there is less regularity 

 of outline. 



On the floating leaves of P. americanus collected early in August were found eggs 

 of Paraponyx and of chironomid." Those of Paraponyx covered broad areas of the 

 under surfaces of the leaves and presented the appearance of minute six-sided cells of 

 honeycomb, yellowish in color. In a few days the larvae hatched and began at once to 

 feed and to cut portions from the leaves for .larval cases. Fryer (1888), in connection 

 with his studies on P. fluitans, mentions that the larvae of Nymphula {Hydrocampa 

 potamogaia) entirely destroy the floating leaves of this species, and thus indirectly 

 induce the development of fascicles of leaves, structures which are analogous to the 

 winter buds of P. ohiusijoliiis. The eggs of the chironomid, which were found on the 

 leaves of P. americanus, were inclosed in small elongate cases blackish in color, suspended 

 from the edges and from the underside of the leaf, and from the petiole. These eggs 

 hatched within a few days, but their entire life history was not observed. 



The leaves of P. ohtusijolius harbor a large number of chironomids, and apparentlv 

 offer a valuable supply of food to many of them. A few of the lar\'se were segregated 

 in small dishes and supplied with fresh leaves of this Potamogeton. An undescribed 

 species of Chironomus was reared. Cricotopus trifasciatus and Tanypus flavellus were 

 the most abundant species on the leaves. 



Other plant parts besides leaves were eaten. The tubers of P. pcctinalus and the burs of 

 P. cris pus were devoured by the larvae of Paraponyx and by the larvae of the Chironomidae. 



The underground stems of P. peclinatus * are provided with large and numerous 

 air spaces (fig. 66), and these were found to be an important air-supplying source for 

 the Donacia larvae. The lar\'ae attached to the subterranean stems of this Potamogeton 

 were collected from the muddy substratum at North Fairhaven August 14, 1913. 

 Stems on which the larvae were not attached showed, quite generally, the characteristic 

 punctures, or double scars, made by the caudal spines in tapping the air supply. 



Jepson (1905) called attention to the value of the tubers of P. pectinatus in the 

 diet of our wild game birds. He says, "The diving ducks, such as the canvasback 

 and broadbill, eagerly seek these tubers, devoting most of their time to this pursuit 

 until the duck-shooting season opens." McAtee (191 1) and Thompson (1913) in their 

 researches on the diet of wild game birds have shown that a large percentage of the 

 food taken is Potamogeton. 



The stomach content of 5 canvasbacks has come under my observation recently. 

 One duck shot in October had been feeding in rich aquatic meadows where Potamo- 

 getons flourished with Myriophyllum, Elodea, etc. Its stomach was filled exclusively 

 with tubers of P. pectinatus. Four ducks shot at the close of the season in January 

 had apparently exercised a choice in the matter of food. Feeding in an abundant 

 mixed vegetation, they had selected only Potamogeton — P. Fresii and P. pusillus. 

 The parts of the plants available were the winter buds which at this season have 

 settled in the mud at the bottom along with the hibernacula of Myriophyllum, Elodea, 

 and other aquatic plants. 



a Durinesubsequentobservationsinjune, 1914, masses of eggs almost infinite in variety and number have beenfound attached 

 to the stems and leaves of the various Fotamogctons. It would seem that these plants, diverse as they are in habit and form. 

 offer especially suitable conditions for the attachnjent of the eggs of aquatic animals. The eggs of the water mite ( Hydracarina) 

 are exceedingly abundant. The eggs of insects that have been recognized are as follows: Stratiomyiidae, Coriscidae. Gyrinidse, 

 Donaciin^e, HydrophylidEe. Pyralidae. Cordulinje (Tetragoneuria), Hydrobatidse and Tricoptera. 



& since this observation was recorded Donacia larvje have been found on the tmderground stems of P, americanus. 



