188 J. O. HAGSTBOM, CRITICAL RESEARCHES ON THE POTAMOGBTONS. 



found only as rudiments. The inner side-nerves run along the midnerve nearly up 

 to the middle before bending out into the lamina. Ligules brown, long, transient 

 and with very low ridges at the base. The colour of the foliage often has a 

 prasinous tone and decajing a yellowish or brownish-green touch. The peduncle 

 sometimes has the same thickness as the subjacent internode, but is more often 

 a little thicker, however without the characteristic incrassation present in P. lucens 

 and its hybrids. Pollen spheric and rather small-grained; style conspicuous and 

 a little swollen; stigma small, oval, but often deformed and elongated as in the 

 fig. 95, E, which seems to be the cause why the species rather often fruits scarcely, 

 with only a few nutlets in the spike. Fruit usually large with prominent dorsal 

 keel but the species varies also with less fruits just as the bulk of the species. 

 The turios are rhizomatic and correspond nearest with those of P. alpinus. They 

 are first described by Royer (F1. Cote D'Or, 1881, 520) and figured in Gluck, 

 Wasser- und Sumpfgew., II, 1906, t. VI, f. 73. Different fruit-forms are figured in 

 Linnsea 1827, t. VI, figg. 22, 23, 24, 26. Stem-diagram, vide Raunki^r 1. c, 274, 

 f. 9. Reichenbach, Icones vol. VII, 1845, t. 49, f. 88, may be, according to Fryer 

 and Fischer, the hybrid lucens X nutans; t. 48, f. 87, seems to me to represent a 

 form of P. alpimis. 



The species varies with elongate laminae (river-form): var. Billolii (Sch.) and 

 occur also as land-form: f. terreslris Gluck. Besides, Fischer has distinguished a f. 

 spathulif alius, a f. brevifolius, and a f. latifolius the caracteristics of which are expressed 

 in the very names, and even a var. lacustris in habit similar to P. natatis. — 



An extreme form of the var. Billotii is gathered in the Zambeze River, Rhodesia: 



f. angustissimus Hagstr, ap. R. E. Fries, 1. c, p. 186. 



Folia omnia angusta, submersa angustissima. P. fluiians Roth. f. elongatus 

 KuEHN, ap. Abromeit, Bericht etc. in Schr. Phys. Ok. Ges. Konigsb. 1893, 43? — 



In the collections of the museums there is a form of Ustin, gathered by Ulehla, 

 with obviously small leaves, which, however seems to be a true P. nodosus. I name it: 



f. moravicus n. f. — Folia submersa et natantia parva. 



I have also seen this form from Turkestan (»Pr. Chan-ova inter Hurw novam 

 et Hurw antiquam, 1884, A. Regel, Iter turkestan.» labelled P. polygoni f alius ?). — 



In the University Herbarium of Upsala there is a plant, labelled s>Pl. ind. or. 

 (Mont. Nilagiri) Ed. R. F. Hohenacker. 1312. P. nutans L. — Steud. Prope Utaca- 

 mund Jun. m.» which I have referred to P. nodosus. Others regard it as P. indicus 

 RoxB. or P. Boxhurgliianus Schultes. The anatomic diagram of the stem corre- 

 sponds with the anatomy of P. nodosus, and its other properties seem to me to deviate 

 rather slightly from the type. Fruit is lacking in those specimens and likewise in 

 specimens from the same station, gathered by Prondloch in 1902 (lib. Haun.). Any 

 complete description of the fruit is not given either in Roxburgh, F1. Ind., or in 

 Schultes, Mant. 1827, but the description of the submersed leaves seems to answer 

 well to a plant from Roxel Dacca (hb. Haun.), which must be referred to the ^mp?i- 

 folii. Its stem-anatomy is: ep. + pshp. + cort. str. in 2—3 circles + 0-, or — Z7-end. 

 + CC of trio-type. 



