202 J. O. HAGSTEOM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



P. fragillimus n. sp. 



P. lucens L. var. 5 jloridanus Ar. Benn., in Graebner, Potamag., 1907, 79 & 161. 



This species differs from all the other Lucentes by the following characteristics : 

 Stem simple up to the primary spike, from which it prolongs after the B- or X)-type. 

 Anatomy: epid. + one-layered pseudohp. + subepid. strands + ligular bundles + u-end. 

 Central stele of trio-type (= P. illin.). Leaves all short, short- petioled, slightly 

 cuspidate, 7— 9-nervecl with short nerve-spaces; mid-vein not much lacunous; lateral 

 nerves joining the midvein in the leaf-apex like gramineus (fig. 102, H — L). Denti- 

 culation extremely fugacious. Ligules lowly bicarinate, 7-nerved in the front-field. 

 The fruits I have seen are malaianus-Vike with dorsal keel, ventral curvature, and 

 apical rostrum as in fig. 115. 



The plant examined was gathered in Guatemala, Laguna de Ayarza, dep. Jalapa, 

 alt. 8,000 ped, 1892 by Heyde & Lux (hb. Haun.). 



P. macropliylloides n. sp. 



Caulis raetralis teres, internodiis longis, simplex v. subramosus. Folia anguste 

 lanceolata, caulina 20 — 25 cm x ±20 mm, denticulata cuspidata petiolata, petiolis 

 ±20 mm longis, typice ll-(13)-nervia; sine phyllopodiis; folia coriacea non observata; 

 nervus medius lacunosus; spatia internervalia rhomboidea (vide fig.). Ligulce tenues 

 longissimse, 80—90 mm, obtusse bicarinata?, carinis inferne humilibus. Peduncvlus, 

 spicce, fructus non visi. — Anatomia caulis, vide infra! — Fig. 100, A, B, C. 



Anatomy: Stem-epidermis of rather short cells, generally 2 — 3 times as long 

 as broad. Along the epidermis there is a one-celled strengthening la3'er and no or 

 few subepidermal bast bundles. Inside we meet with 1 (2) circles of bast and 

 vascular bundles. The central axis is surrounded by a typical C7-endodermis and 

 besides endowed with 4 (2) median bundles and 3 (2 — 3) lateral ones on either side, 

 all with non-fused xylem canals. The lacunar part of the leaf round the central 

 vascular bundle is destitute of interlacunar as well as subepidermal strands. 



The habit of this plant is much like that of P. lucens v. longijoUus. Stem 

 with long internodes, simple or with rudimental branches and long-lanceolate leaves, 

 all of which are narrow and petioled. The first and second rank veins fork as the 

 figure shows. For the form of the apex and of the nerve-spaces I refer to the figure, too. 



At the base of every shoot there are two sheaths, after which follows a narrowly 

 lanceolate leaf, not as in P. lucens a phyllopodium, of which this species as it seems is 

 void, just as it is also void of the ZMce?i.s-inclination to diminishing the blades from 

 both ends. Only the midnerve portion is lacunous but lacks mechanic tissue, because 

 of which the leaves are soft and not rigid as in P. lucens. Ligules very long, the 

 ridges of about the same height as the thickness of the ligule, thus considerably lower 

 than in P. lucens, which has the ridges 3 — 4 times as high as the thickness of 

 the ligule (fig. 110, B). 



