132 



J. O. HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOQBTONS. 



different ranks. Further it is said to have 5 — 7-nerved small floating leaves (24 — 13 

 X 8 — 2 mm) and submersed leaves with the size of 52 X 1 mm, for the rest described 



thus: utrinque attenuata apice acuminatissima, margine scepe 

 undulata, juxta nervum medium nervis dehilibus valde approxi- 

 matis utrinque binis prcedita etc. The last statement might 

 concern the dark lines near the midrib, which easily can be 

 seen by an ordinary magnifying glass and which properly desig- 

 nate the site of the partition-walls of the two largest lacunae. 

 I have not seen this plant from Java, but all specimens, hit- 

 herto held for P. javanicus, possess in the submersed leaves 

 a lacunar system extending over the middle of the leaf from 

 side-nerve to side-nerve. A cross-section of the leaf shows 3, or 

 more frequently 4 rows of lacunae on either side of the lacu- 

 nulee round the mid vein. Such a lacunar system P. cristatus 

 also possesses, and even the form and nervation both of the 

 submersed and floating leaves coincide in the two species. The 

 floating leaves are at full development always 7-nerved, but 

 the utmost pair of nerves run so near to the marginal bast- 

 bundle, that they sometimes, to the naked eye, seem to be 

 confluent with it, the leaves thus becoming falsely 5-nerved. 

 P. quinqueriervius m. has also exactly a similar nervature in 

 the floating leaves. — The ligules are open and convolute, 

 5 — 6-nerved in the front-field. They remind much of those of 

 P. trichoides and their internal structure is the same in the 

 intercarinal part having much smaller cells on the inner than 

 on the outer surface. 



The pistils are characterized by the broad, keeled ovary 

 and narrowly oblong stigma. The fruit has prolonged rostrum 

 and a dorsal keel with obvious small bosses. 



Of the materials here accessible the Wilford specimens of 

 Corea seem to correspond most strictly to the description, 

 whereas the African materials pretty much deviate from it, 

 for instance by broader but softer leaves, longer internodes, 

 different mode of prolonging the stem (cincinnately not dicho- 

 tomously), longer peduncles etc. The species seems to form 

 numerous turios, as to form corresponding with the turios 

 of P. miduhikimo. They consist of small, transformed, narrowly 

 fusiform branchlets with 2 — 3 angulary spreading, short, 

 sharply pointed external leaves, and many inner ones wholly 

 clasped by the sheaths, which together with the leaves form 

 a protracted sharp point. 

 Stem terete or nearly so. Its epidermis lacking (Corean and Japanese forms) 

 or possessing (African and Indian specimens) a one-celled hypodermatic stratum; 



Fig. 58. P. javanicus Hassk. 

 A, Top of a submersed stem- 

 leaf, y. B, Transverse section 

 of the same below the middle 

 (material from Madagascar) m, 

 midvein, n' , lat. nerve, ^y**. C, 

 Ti'ansverse section of a sub- 

 mersed stem-leaf {Corean ma- 

 terial), '{'». D, Turio in a leat- 

 axil, somewhat enlarged; Ej 

 Pistil, side-view, ^^. F, Trans- 

 verse sect, of a young ligule 

 at the base, \^, ic, front-lield. 



