170 



J. O. HAGSTROM, CRITICAL- RESEARCHES ON THE POTAMOGETONS. 



late, 55 X 4 mm, sessile, tapering at both ends, 3-nerved, obtuse; ligules thin whitish, 

 about 10 mm in length. Peduncle not incrassate; spike 1,5—2 cm long. Style short 

 but conspicuous; stigma rounded. A close relationship is assumed between this species 

 and the N. American P. Nuttalii, but neither the style and fruit nor the stem-ana- 

 tomy suggest such a relation. Fruit with low dorsal keel and elongate recurved beak, 

 ventral face prominently convex and so are also the sides. Embryo curved in usual 

 manner. 



Anatomy of stem: Epidermis without strengthening layer and strands, cortical 

 bundles absent and the central stele four-bundled encompassed by an 0-?7-endodermis. 



Distribution. Brazil, Minas Geraes, Gongo Secco (lib. Bero- 



B lin.). Beside P. Ulei it seems to belong to the higher mountain 



regions and might also be met with in the western alpine States. 



P. repens Hagstr. ap. R. E. Fries, Bot. Unters. in Wiss. Ergebn. 

 schwed. Rhod.— Kongo-Exp. 1911-12,1, 1915, 185, f. 15. — Fig. 87, 88. 



Rhizoma repens teres 1 — 2 mm crassus (in diam.). Caulis 

 teres, 1 mm in diam. simplex vel pauUo ramosus internodiis brevis- 

 simis (infer. ± 5 mm). Folia tenuia canaliculata, typice 7-nervia 

 linearia sessilia integerrima subacuta (inf. 50 — 60 X 2 — 3, superiora 

 90 X 3 — 4 mm). Nervatura vide fig. Ligulce membranacese tenues 

 caducse ± 20 mm longae subbicostatse. Spicae desunt. 



Anatomy of the stem: Epidermis-cells of usual form, 3 — 5 

 of 'snbmoised leaf, s^'. timcs as long as broad. The epidermis is strengthened by a one- 

 c' Transverse section of Celled pscudo-liypoderma and scattered small bast- bundles (see the 

 tlateVbtiTie!'™'^'"' f^g- §7, C). Cortcx of usual structure. Lacunar system of three 

 circles of lacunae. True cortical bundles absent. Endodermis of 0- 

 cells. The central cylinder exhibits two median bundles with common xylem cavity 

 on either side of which there is a lateral bundle. Mechanic tissue as the figure shows. 

 The rhizome differs in the usual way by free bundles in the central cylinder, 

 smaller lacunse of about equal size among themselves, and a two-layered hypoderma 

 with few mechanic cells. 



The leav^es are 7-nerved, linear, tapered at the base and top, gutter-shaped. 

 Internal structure and lacunar system as the figure shows. The specimens examined 

 were young plants and it is therefore not known to me if P. repeals can produce 

 floating leaves or not. Ligules 7-nerved in the front-field, apex obtuse. Intervaginal 

 scales lanceolate 1 mm long, seven or more in number. 



The course of the subepidermal strands of the stem and that of the bast and 

 vascular bundles of the leaf and ligule is shown by the longitudinal section through 

 a node figured below. The subepidermal strands generally do not continue in the 

 wing-fields of the ligule, but that organ has its own bundles, which descend through 



Fig. 86. P. saero- 

 carpus ScHUM. A, Top 



