. Critical researches on the potamogetons. KUNGL. SV. VET. AKADEMIENS HANDLIN6AE. BAND 55. N:0 5. 199 a few (rarely no) subepidermal strands. Inter]acunarly there is always to be found the ligular circle of vascular and bast bundles and mostly scattered bundles inside it. The endodermis consists of M-cells, generally well developed, and of a laterally compressed form very much like those of P. graynineus. In the central axis there are alwaj's two large median xylem cavities separated from each other by mecha- nical tissue. Otherwise the arrangement of the bundles varies from diagrams of trio-
. Critical researches on the potamogetons. KUNGL. SV. VET. AKADEMIENS HANDLIN6AE. BAND 55. N:0 5. 199 a few (rarely no) subepidermal strands. Inter]acunarly there is always to be found the ligular circle of vascular and bast bundles and mostly scattered bundles inside it. The endodermis consists of M-cells, generally well developed, and of a laterally compressed form very much like those of P. graynineus. In the central axis there are alwaj's two large median xylem cavities separated from each other by mecha- nical tissue. Otherwise the arrangement of the bundles varies from diagrams of trio- type to those of eight-bundled type, and the lateral bundles are sometimes reduced in number. Two aberrant forms may be established: f. rosulatus n. f.: — Rami primee ordinis rosulati internodiis brevissimis. iV. America: Florida, leg. O. Vesterltjnd. f. homopliyllus n. f.: — Folia omnia submersa, Fig. 99. P. aiinoensis Morong. A, Top of a snbmersed leaf (somewhat enlarged). B, Top of a floating leaf showing the blunt, broad muoro and the nervation (a little enlarged). C, Part of an anatomical stem-diagram str, subepidermal strands, X, occasionally occurring bundles in the bark, \°. This form is destitute of floating leaves, even at the secondary spikes. Occurs in Mexico, State of Michoacan, Lake Patzcuaro, 90, Pringle (hb. Stockholm.), label- led »No. 3327 P. Zizii Roth». Texas, Drummond, 3d coll., no. 272 (hb. Lund.). Pine Lake, Mich., 92, Wheeler (hb. Haun.) P. illinoeiisis Mor. x luceiis L. (P. pseuclolucens n. hybr.). Folia omnia submersa, ad formam ut in P. lucente, ad nervationem vero iis P. illinoensis Dr. T. MoRONG, who collected the plant here concerned, has determined it as P. lucens. Undoubtedly this species is also present in it with some properties. Especially obvious are the sharp leaf-tips, but the petioles also and the leaf-shape bear witness of P. lucens. On the contrary, the ramification of the nerves is more like that which i
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