KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. NIO 5. 



199 



a few (rarely no) subepidermal strands. Interlacunarly there is always to be found 

 the ligular circle of vascular and bast bimdles and mostly scattered bundles inside 

 it. The endoderrais consists of i^-cells, generally well developed, and of a laterally 

 compressed form very much like those of P. gramineus. In the central axis there 

 are always 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 primse ordinis rosulati internodiis brevissimis. 



N. America: Florida, leg. O. Vesterlund. 



f. lioniopliyllus n. f. : — Folia omnia submersa, membranacea. 



Fig. 99. P. illinoensis Moronc;. A, Top of a snbmersed leaf (somewhat 

 enlarged). B, Top of a floating leaf showing the blnnt, broad mucro and 

 the nervation (a Iittle enlarged). C, Part of an anatomical stem-diagram 

 st)-, subepidermal strands, X, occasionally oceurring bundles in the bark, s 1 °. 



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. illinoensis Mor. x lucens L. (P. psendolucens n. hybr.). 



Folia omnia submersa, ad formam ut in P. lucente, ad nervationem vero iis 

 P. illinoensis simillima. 



Dr. T. Morong, who collected the plant here concerned, has determined it 

 as P. lucens. Undonbtedly 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 is characteristic of P. illinoensis, besides which the rather short 

 (30 — 35 mm) ligules, narrow nerve-spaces, and the anatomic stem-diagram belong to 

 the just mentioned species. All the leaves, also the topmost ones, are constructed 

 as submersed leaves lacking stomata. On the other hand the topmost leaves remind 



