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



137 



P. spirilliformis n. sp. - - Fig. 60, D-I, 61, A-c. 



Caulis teres — subteres, ramosus, ramis subrecurva- 

 tis, a spica primaria ramis saepe cincinnatiforme valde 

 prolongatus. Folia natantia apice rotundata obovata, 

 7— 10-nervia, petiolata evaginata, petiolis lamina breviori- 

 bus, laminis 20 — 25x5 — 8 mm; submersa linearia incon- 

 spicue trinervia, obtusiuscula, 10—30 X 1 mm, vaginata, 

 ligulata. Pechmculus spica brevior, 1 — 2 mm longus. Spica 

 brevis, fructifera 3 — 5 mm longa, 4 — 6-flora. Fruetus 

 parvus 1,2 — 1.5 x 1 — 1,25 mm, rotimdatus, a latere com- 

 pressus, 3-carinatus, carinis gibbosis, brevissime rostra- 

 tus. Embryo 1 l /s circulis curvatus. 



The stem-anatomy differs from that of the nearest 

 related species by the absence of subepidermal bast. The 

 necessary strength is obtained by the short epidermis-cells, 

 in general only 2—3 times as long as broad. From P. 

 dimorphus, with which it can easily be confounded, it 

 differs by the usually obovate floating leaves, the straighter 

 lower branches, the short upper peduncles, and few-flow- 

 ered short upper spikes and, above all, by the fruit being 

 somewhat beaked, smaller, and with a less prominent 

 dorsal keel, but with low and a little prickly lateral keels, 

 which are absent in P. di?norphus, the fruit of which on 

 both sides of the dorsal keel presents a smooth roundness 

 corresponding to the form of the embryo. The colour of 

 the fruit is olive-brown. 



The stem is destitute of subepidermal bast. 



The sheaths and ligules of the submersed leaves of 

 this and the coordinate species are figured close by. In P. 

 dimorphus the ligule is truncate or subemarginate, open, 

 and nearly nerveless in the front-field; the leaf-sheath 

 usually connate, seldom open. In P. spirilliformis the 

 ligule and sheath are always closed, the ligule usually very 

 slightly emarginate and 2 — 5-fibrous in the front-field. 

 P. diversifolius has usually a streched narrow ligule in 

 form and strueture, besides, nearly like that of P. 

 spirillif. P. conjurigens m., lastly, has the ligule more or 

 less open above and the tip more or less roundish- 

 truncate. 



Distribution. Brazil, Rio grande do Sul, 92, Lindman 

 (hb. Stockholm). Uruguay, Vera, 01, Berro (hb. Haun.). 



K. Sv. Vet. Al<ad Handl. Band 55. N:o 5 



Fig. Gl. P. spirilliformis Hacistk. 

 A, Transverse section of the stem, 

 lov/ét part, 4 /. B, Transverse sectioti 

 of the stem-prolongation, 4 r c , vase. 

 bundles of the stele hatched. C, 

 Young sheath, /, ligular part, bl, blade, 

 basal part, i, insertion line ; the dotted 

 line above designates the variation of 

 the incisure, y. A -^> ^» Correspond- 

 ing organ of P. dimorphus, P. con- 

 jungens m. and P. diversifolius resp. 



C, D, a, F, baek-view, E, side-view, 



D, b, split. 



18 



