33 
16. POTAMOGETON PERFOLIATUS, L. Sp. Pl. 126 (1753). 
Stems slender, from running rootstocks which throw up many 
shoots, much branched, often with many short lateral branches 
along the main stem. Leaves very variable in shape and size, 
mostly ovate or rounded, sometimes lanceolate, usually obtuse, 
sometimes acute at the apex, amplexicaul and cordate at base, 
meeting around the stem. They are never cucullate, as in the 
preceding species, and never known to produce propagating buds 
or glands. They are often crowded upon the stem, but more 
commonly separated at a considerable distance, generally alter- 
nate, but opposite under the nodes of the branches. The typical 
European forms have large rounded or ovate leaves about 2 inches 
long by 116 inches broad, varying from this to narrow and elon- 
gated forms %-1% inches long and 4-15 lines in width, and 13- 
27-nerved. The full type is rather rare in this country, the greater 
part of our forms being small leaved, and west of New England run- 
ning into the form known as Var. /anceolatus, Robbins. As found 
here the typical plant has leaves varying from 5 to 15 lines long 
and from 3 to 12 lines wide, usually obtuse and minutely serrulate 
near the apex. Peduncles 114 inches long, about the same thick- 
ness as the stem, usually erect or slightly spreading, running in the 
axils of the leaves for a long distance along the upper part of the 
stem. Spikes 8-12 lines long, often flowering and fruiting under ` 
water. Fruit obliquely obovate, 114—114 lines long by 1 line ora 
little more in breadth, obscurely tricarinate on the back, the face à 
little curved outwardly towards the top, the sides with a shallow 
indentation which runs into the face; style nearly facial; embryo 
slightly incurved or with its apex pointing directly towards the 
base. 
Var. RICHARDSONI1, Ar. Bennett, Jour. Bot. xxvii. 25 (1889). 
Var. lanceolatus, Robbins, in A. Gray, Man. Ed. 5, 488 (1867). 
Mr. Bennett notes that the name of Robbins is preoccupied by 
a different form of Blytt in Norges Flora (1861), and proposes the 
present name in honor of the Arctic explorer, Dr. Richardson, 
* who seems to have been the first to point out the difference from 
the European forms in the * Appendix’ (Botany) to Franklin's Ex- 
pedition." 
