132 



J. O. HAGSTRÖM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



different ranks. Further it is said to have 5 — 7-nerved small f loating 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 debilibus 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 lacuine. 

 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 över 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 lacuna3 on either side of the lacu- 

 nula? round the midvein. 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 ahvays 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 



the leaves thus 



becoming 



falsely 5-nerved. 



confluent with it, 



P. quinquenervius m. has also exactly a similar ncrvature 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 interna! structure is the same in the 

 intercarinal part having much smaller cells on the inner tlian 

 on the outer surface. 



The pistils are characterized by the b ro ad, 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 (cineinnatelv not dicho- 

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

 numerous turios, as to form corresponding with the turios 

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

 fusiform branchlets with 2 3 angulary spreading, short, 

 Bharply pointed external leaves, and many inner onea wholly 

 clasped by the slioaflis, whieh together witli t ho leaves form 

 a protracted sliarp point. 

 Stem terete or nearly so. Ils epidermis laeking (Corean and Japanese forms) 

 or posseesing (AfrioaD and Indian tpeoimens) a one-oelled hypodermatio stratum; 



Rg. 58. /'. javantcui Bassk. 

 i, Top "i a sabmersed Btem- 



i' ;.t. ;•. /;, Trann ei m section 

 .,i iii. tame below the middle 

 i i.il from Madagaaoar) m, 

 roidi 'in, a' , lat. uerve, ' ','". C, 

 Transri i le a ction of a miI>- 

 iii. i k .i -i. in ]■ .if i< loreao ma- 



i o, ' ;'" /'. Tunn in a l. af- 



axil, BOmewhal ■nlarged; B, 



Pistil, Bido-view, ','. /•'. Trana- 



seot. ■>! a jronng I i^;ii lo 



ut 1 1 1 • i..i e, V " . ii"nt fleld. 



