44 



Professor Macoun's^ much older record from the Canadian side 

 at Niagara, furnishes conclusive evidence that this pondweed 

 has for some years been well established westward. Indeed, it 

 may be added that Professor Henry Costing, who made the 

 Black Lake and Pigeon Lake collections in Michigan, has 

 written me that in 1928 he collected P. crispus in Lake Minne- 

 tonka, Minnesota, though at the time he received my inquiry 

 he was not able to find his specimen. 



The time when P. crispus was first brought to the North 

 American continent, and the place in which it found its first 

 foothold, must of course remain conjectural. With the excep- 

 tion of the two Americas, it is of nearly world-wide distribution, 

 ranging through most of Europe, thence across Asia to Japan 

 and Korea and southward into Africa and Australia. According 

 to Arthur Bennett,^ the oldest dated American specimen is 

 labeled "Philadelphia, 1841-2. Gavin Watson & Kilvington," 

 though "one from Delaware .... is probably older; it was 

 collected by R. Eglesfeld Griffith, of Philadelphia." It appears 

 certain that this plant has been in American waters for a cen- 

 tury — perhaps much longer — and its abundance in the East, 

 shown by the preponderance of collections from that region, 

 indicates that it may have become established there first. 



Its subsequent spread westward might be attributed to a 

 variety of agencies, but it seems to me most likely that aquatic 

 birds have been the most important. There are more than 50 

 species which regularly visit the United States for some part of 

 each year; those that breed commonly in the Northern States 

 are of 19 species; and those that breed far northward but winter 

 in the States number more than 20 species. For 16 important 

 species of game ducks, McAtee^ reports that pondweeds con- 

 stitute from 4 to over 40 per cent, of the food and that the 

 average proportion of pondweed in the food of these species i's 

 13.88 per cent. 



Commonest among our ducks is the Mallard. Wintering 

 chiefly in the southern half of the Mississippi Valley, but also 

 casually as far east as Massachusetts, it breeds in the summer 

 throughout a large territory ranging from the northern States 

 far into Canada. The Canvasback, formerly much more abun- 



6 Jour. Bot. 39: 201. 1901. 



6 U. S. Dept. Agr., Biol. Survey. Bull. 81. 1911. 



