DESCRIPTION OF SPECIES— AEACE^. 103 



ing from it. From this it seems that the identity of these plants of Point 

 of Rocks and of those described by Prof. Dawson is not positively ascer- 

 tained. In my opinion, they represent the same kind of vegetables, and are 

 referable to the following species, with which they are mixed. 

 Habitat. — Point of Rocks {Dr. F. V. Hayden). 



SPADICIFLOR^. 



ARAOE^. 



PISTIA, linn. 

 Pistia corrugata, Iiesqz. 



Plate LXI, Figs. 1, 3, 4, 6, 7, 9-11. 

 PUtia corrugata, Lesqx., Annual Report, 1874, p. 299. 



Leaves broadly obovate, incrassated from the middle toward the base, bordered upward by a 

 wavy margin, gradually narrowed into a sbort pedicel with bundles of radicles at its base; veins 

 going out from the pedicel in two or three compact fascicles, dividing in passing up from the base of the 

 leaves, and forming, by cross-brancblets, large irregular polygonal meshes. 



The leaves, round when young, are, when fully developed, broadly 

 obovate or round at the upper border, gradually narrowed from the middle 

 downward to a short pedicel, varying in size from two to six centimeters 

 long and from two to four centimeters broad; nei'vation distinct, formed by 

 the subdivision of veins, inflated into the pedicel, and dividing irregularly, in 

 more or less dichotomous branches, in ascending to the borders, forming, by 

 nervilles, oblique or in right angle, distinct quadrangular areote, which 

 become smaller and quadrate along the borders. The lower part of the 

 leaves appears inflated or thickened, and is generally surrounded by a 

 deep line, the inside of which is slightly convex, and passes around and 

 under a flattened border whose areolation is generally more distinct and 

 smaller. This line is more or less discernible upon most of the specimens, 

 which are very numerous; but sometimes it is marked near the base only, 

 as in figs. 1, 4, 6, 7, and, when passing up, disappears into the meshes of the 

 areolation along the inside line of the flat borders. Sometimes, as in fig. 3, it 

 is more deeply marked upward, and disappears on the sides, leaving the 

 lower part inflated as far down as the pedicel. In small, apjiarently young 

 leaves, as in fig. 1, the circular line is less distinct, and its internal part does not 

 seem inflated; even in very small leaves the borders are not separately traced, 

 and the nervation i.s not disconnected from the base to the circumference. 



