1908] Fernald,— Lists of New England Plants,— XXII 171 
C. & S) in its larger floating leaves (29-41-nerved), its broader sub- 
mersed leaves (9-13-nerved) and its large fruit (3.5-4.5 mm. long). 
P. filiformis Pers. occurs locally in northern Maine and northern 
Vermont. In Maine and Quebec it is apparently confined to shallow 
ponds and streams with marly bottoms, and it should be sought in 
such situations in northern New Hampshire. 
P. gemmiparus Robbins is frequent in slow streams and pools 
through southern Maine and it occurs in eastern and central Massa- 
chusetts, Rhode Island, and northeastern Connecticut. It should, 
therefore, be found in southern New Hampshire. 
P. heterophyllus Schreb. The different forms are apparently due 
in great part to the conditions under which they grow and probably 
are all of more general distribution than the herbaria indicate. 
P. interruptus Kit., differing from P. pectinatus in its strongly keeled 
fruit, occurs in brackish waters of eastern New Brunswick and also 
in Michigan. Search may readily show it to be on the New England 
coast as well. 
P. lateralis Morong, occurring in eastern Massachusetts and in 
northern Connecticut, is to be sought, naturally, in Rhode Island. 
P. obtusifolius Mertens & Koch, frequent in north-central Maine 
and in Vermont, should be sought in northern New Hampshire. In 
Maine it prefers clear cold streams. 
P. polygonifolius Pourret, a common species of Eurasia, Greenland, 
and even of Africa and Australia, occurs in Newfoundland and on 
the coast of Nova Scotia. It has the aspect of a very reduced P. pul- 
cher, with extremely slender spikes, the tiny fruits being only 1.5-2 
mm. long. It is to be watched for in eastern Maine. 
P. pulcher Tuckerm. his distinct species is frequent in eastern 
Massachusetts, and it is known from southern Maine and from 
Brattleboro, Vermont (according to Morong). It is, therefore, to 
be expected in southern New Hampshire. 
P. pusillus L., vars. polyphyllus Morong and Sturrockii Вепп., 
likewise, should be looked for in southern New Hampshire. 
P. rutilus Wolfgang, one of our rarest species, is known from the 
St. Francis River in northern Maine and from a single station in Lake 
Champlain. It resembles very slender extremes of P. pusillus, but 
has much longer stipules, which are persistent and rather conspicu- 
ous; and its sharp-acuminate leaves are almost erect. 
P. Vaseyi Robbins is apparently more common than generally 
supposed and is probably well distributed in southern New England. 
