102 Mr. Getjer's Plants of Illinois and Missouri. 



113. Salix Muhlenbergiana, J115. Salix longifolia, Muhl. 



Willd.116. Salix rigida, Muhl. ? 



114. Salix nigra, Marsh. 



117. Potamogeton diversifolius, Barton, (?. spicatus. This form 

 appears at first view to be a distinct species, characterized by the 

 narrower, only 5-nerved upper leaves, and petioled oval or cylin- 

 dric spikes. P. diversifolius, a. capitatus, the common form, has 

 more oval 7-nerved upper leaves, and nearly sessile few-flowered 

 heads. But sometimes the lower heads of our variety are also 

 capitate and nearly sessile, and the fruit is generally alike. The 

 fruit, or nut, is always compressed, winged on the back, with two 

 lateral carinas, which are generally denticulate, the nut appearing 

 muricate ; and in (9. they are often nearly or entirely undivided, 

 but by no means generally so. The embryo describes 1J of a 

 spiral circumvolution ; the embryo of most other species forms 

 only f, 1 or 1^ circumvolution. I know but one species, P. 

 densus, which exhibits 2£ circumvolutions. 



It may not be amiss here to remind botanists in this country, 

 that the ripe fruit furnishes the best characteristic marks to dis- 

 tinguish the different species of Potamogeton. The fruit, for ex- 

 ample, proves that P. niarinus, Linn, is entirely distinct from P. 

 pectinatus, Linn., with which most authors confound it; P. <ma- 

 rinus occurs not only on the sea-coast, but also in the salt-ponds 

 of the Upper Missouri, (Geyer, in Nicollet's expedition.) Speci- 

 mens of Potamogeton should always be collected with ripe fruit. 



118. Phalangium esculentum. Nutt. 



119. Trillium recurvatum, Beck. 



120. Juncus marginatus, Rostk. 



121. Dulichium spathaceum, Pers. 



122. Cyperus kyllinggeoides, Vahl. 



123. Isolepis capillaris, Roem. & Schult. 



124. Heleocharis tenuis, Schult. 



125. Eriophorum gracile, Koch, in Roth, catalect. 2. p. 259. 

 A species which has frequently been found in the United States; 

 it appears to have been taken for E. anguslifolkim — my speci- 

 mens at least, received from Pennsylvania and from Ohio, were 

 so labelled — but is easily distinguished by its triquetrous, subulate 

 leaves, and the linear yellowish seeds. The true E. angustifo- 

 lium, Roth, is the largest of all the species, with the longest 

 (1$ inch) wool; leaves 1 or 1£ lines broad, channeled; pedun- 



