35 
Since I obtained this from Mystic Pond, Medford, Mass., in 1879, 
I have visited the locality for several years in succession, and, 
though I have always found the plant growing vigorously, yet it 
has shown no signs of prefecting fruit. In the year 1887 I found 
it growing in Miacomet Pond, Nantucket, under water about 3 
feet deep, but it was entirely without flowers or fruit. 
It is closely allied to P. perfoliatus in habit, with which it is asso- 
ciated in growth, but very unlike that in foliage, and scarcely one- 
third as stout in any of its parts. August-September (Plate XLI). 
18. POTAMOGETON CONFERVOIDES, Reichb. Icon. Fl. Germ. et. Helv. 
vii. 13 (1845). 
. Р. trichoides, A. Gray, Man. ed. гр. 457 (1848). Tuckerm. Am. 
Jour. Art and Sci. 2 ser. vii, 358 (1849), not Cham. 
P. Tuckermant, Robbins in A. Gray, Man. Ed. 2. 434 (1856). 
Mr. Bennett states in Jour. Bot. xxviii. 92, that he has seen a 
specimen of this species in Gay's Herb. at Kew under Reichen- 
bach's name, and that it is undoubtedly the same as P. 77 uckermant, 
Robb. The description of Reichenbach corresponds very well to 
our plant. There is here a good illustration of the danger of determin- 
ing names without corroborating specimens, for Tuckerman, one of 
the most minute and careful observers, says in his paper upon P. 
trichoides: “I have seen no specimens of the European plant, but 
Chamisso's minute description, and his figure of the fruit leave little 
or no doubt of the identity of ours with it,” and yet he was mis- 
taken. 
Stem from a creeping rootstock, slender, terete, much-branched, 
the upper branches repeatedly dichotomous, 6-18 inches high. 
Leaves very delicate, flat, setaceous, 1-234 inches long, the 
broadest scarcely Y line wide, tapering to a long hair-like point, 
1-3-пегуед, often with a few cross ribs or coarse reticulations, of a 
bright green color, a little yellowish tinted. Stipules delicate, 
obtuse, 2-3 lines long. Peduncles terminal, 2-8 inches long, straight 
and erect, somewhat thickened upwards, sometimes with a short 
lateral branch bearing a spike. Spikes capitate, 3 or 4 lines long; 
Fruit thick with a shell roundish-obovate, 1—1 14 lines long and about 
as wide; back sometimes a little angular or sinuate, 3-keeled, the 
middle keel sharp and prominent; face notched near the base ; 
sides impressed with a shallow indentation which runs into the 
