A REVISION OF THE AMERICAN LEMNACEAE. 4l 
slightly convex, gradually rising at the acute apex like the 
bow of a boat; under surface gibbous; floating at the sur- 
face of pools with the entire upper surface of the frond 
exposed to the air; stomata numerous; profusely punctate 
throughout with brown epidermal pigment cells. Upper 
portion of the fronds consisting of small celled tissue, and 
the lower of large cells. ‘‘ Utricle ellipsoidal ’’ (Grise- 
bach). Flowers and fruit unknown with us.— Occurring, 
in our range, east of the Mississippi river, from the Lake 
region to the Gulf of Mexico.— Plate 4 E. 
This species as well as our North American plants have 
heretofore been referred to W. Brasiliensis Wedd. In 
comparing our form with Weddell’s original material, as 
well as his description * of the species, I find a marked 
difference in the more elongated and less gibbous fronds, 
the upturned acutish apex and more numerous pigment cells. 
Specimens examined from Ontario (Payne); Michigan (Bigelow, 
1867); Illinois (Hall, 1867; Eggert, 1891); Tennessee (Gattinger). 
#* * Globose to ellipsoidal, not punctate. 
Wourria Cotumbrana Karst. Bot. Unters. 1: 103. 1865. 
Fronds ellipsoidal to globose; symmetrical; upper sur- 
face convex with usually about three small inconspicu- 
ous papules in a row along the median line; .54-.3 mm. 
wide and deep by .48-1 mm. long; floating at the surface 
of the water with only a very small portion of the upper 
surface exposed to the air. In this area are to be found 
but a few (1-10) stomata. Pigment cells none. The 
body tissue is uniformly large celled throughout.— Oc- 
curring abundantly in ponds throughout the eastern half of 
‘Canada and the United States.—Plate 4F. 
Specimens examined from Ontario (Payne; Gillman, 1869); Massa- 
chusetts (Robbins, 1870); New York (Craig; Austin, 1866); New Jersey 
(Austin, 1867); Pennsylvania (Parker, 1863; Crawford, 1894; Kront, 
1894); South Carolina (Ravenel, 1872); Florida (Curtiss); Michigan 
* Weddell, H. A. Observations sur une espéce nouvelle du genre 
Wolfia. Ann, Sci. Natur. III. 12: 170. 1849. 
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