170 



.T. O. HAGSTROM, CRITICAL RESKARCHES ON THE POTAMOGETOXS. 



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

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

 but conspicuous; stigma rounded. A close relationsbip 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-C7-endodermis. 



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

 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 paullo ramosus internodiis brevis- 

 simis (infer. ± 5 mm). Folia tenuia canaliculata, t} 7 pice 7-nervia 

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

 90 X 3 — 4 mm). Nervalura vide fig. LiguUv membranacea? tenues 

 caducae ± 20 mm longse subbicostata?. Spicoe desunt. 



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

 times as long as broad. The epidermis is strengthened by a one- 



Fig. 86. P. sclero- 

 carpus Bchum. A, Top 

 of snbmersed leaf, •',". 



c, Transverse aection of celled pseudo-hypoderma and scattered small bast-bundles (see the 

 fig. 87, C). Cortex of usual structure. Lacunar system of thrce 



b, lateral bnndle, 'V'. 



Cortex of usual structure. 

 circles of lacuna?. 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 cqual size among themselves, and a two-layered hypoderma 

 with few mechanic cells. 



The leaves are 7-nerved, linear, tapered at the basc and top, gutter-shaped. 

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

 u erc young plants and it is therefore not known to mc if /'. r< />< ns can produce 

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

 scales lanceolate 1 mm long, seveu 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 show n by the longitudinal section through 

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

 wing-fields of the ligule, but that organ has it s own bundles, w duell deseend through 



