KTTNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55- N:0 5. 



111 



below, showing the mode in which the principal lateral nerves join the midvein in 

 the apex, and how the outer and inner (sometimes missing) secondary nerves join 

 the principal ones. Characteristic is that the principal side-nerves anastomose in the 

 very apex, whereas the condition in P. Aschersonii is different in as much as these 

 nerves unite with the midvein at a leaf-width's distance from the point. Leaf-base 

 almost rounded and the top with a cusp, distinct and sharp especially on the branch- 

 leaves. Ligules open, of usual form; their front-field 8— 10-fibrous. 



Distribution. The species is spread in Chile of South America, but how far 

 beyond is unknovvn to me. — Rio Renaco, 06, Morton Middleton v ^ s t r 



(hb. Stockholm.). A 



P. Aschersonii Ar. Bennett. 



Notes on Potamog., Journ. of Botany, 1893, 294. — P. 

 tenuijolius Phil. in Anal. Mus. nac. Chile, 1891, App. 95, sec. 

 A. Benn. 1. — c. P. pusillus p sphcerocarpus K. Schum. in Fl. 

 Brasil, 1894, 687 is held to be a synonym to O. Berteroanus Phil. 

 (see Asch. & Graebn., Pflanzenreich, Potam. 1907, 118!), but 

 the description of the leaves, »foliis modice latis trinerviis, pallide 

 viridibus in rubellum vergentibus » is more correspondent to the 

 species above; I have not seen specimens though. — Fig. 47. 



P. Aschersonii belongs to the comparatively small species 

 of this group, about 20 or 30 cm high with almost terete capillary 

 stem prolonging itself by spike-bearing branches of 1st — 2nd ( — 3d) 

 rank in the same way as P. panormitanus. Nevertheless I have 

 also seen veritable giant-specimens, which could not be taken for 

 this species without a thorough examination. At a closer research 

 it is, however, evident that it differs more by the bigness of all 

 the organs than in the characteristic properties. See below! 



rr,, • r ... , , . -. Fig. 4G. P. Berteroanus 



Ihe stem is otten capillary and nearly terete, seldom more phil. a, Transveise sect. 

 flattened (3:1). Both the stem and the peduncle are provided bundies/^^bastbunXs! 

 with a one-celled pseudo-hypoderma which organ seems to charac- j^ f f' Top of a stem " 

 terize all the South American species of this group, and besides 

 with strong subepidermal strands. The central cylinder is nearly terete or oval in 

 cross-section with a compound vascular bundle and a common xylem cavity, thus 

 presenting a circular stele diagram, even if the stem is more compressed. In the 

 peduncle this compound bundle dissolves into two (4) bundles as is shown in the figure. 



The leaves are narrow, 1.5— 2( — 3) mm broad and three-nerved, obtuse with a 

 cusp and tapering at the base. The midrib is accompanied by one or two rows of 

 air-lacunae with interjacent sclerenchyma (see the fig.!), which effects a certain stiff- 

 ness like a panormitamis-le&f. The låter alnerves run nearer to the margin than to the 

 midvein, which they join at a distance of a leaf-width from the very point. Ligules 

 of usual shape, 8—10 mm long or more, front-field 3 — 5-fibrous. 



