174 



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



The fruit of specimens from Takapo Lake is obliquely obovate, with a short beak 

 and faint dorsal keel, scarcely 2 mm long by 1,3 mm broad. — Genuine submersed 

 leaves, when occurring, rounded obtuse or slightly emarginate in the apex, nerved 

 as is shown in the fig. below. Midrib lacunous, the two chief lateral nerves running 

 nearer to the margin than to the midrib. Leaf -base narrow and a little sloping; 

 petiole at least in the lower leaves very short or inconspicuous. 



The epidermis of the stem, consisting of somewhat stretched cells, always lacks 

 strengthening layer. Endodermis composed by 0-cells with a very faint tendency 



to one-sided thickening. The cortical 

 bast or vascular bundles now spread 

 toward the epidermis, now appear 

 between the utmost lacunar circle 

 and the next to it. The central 

 cylinder is characterized by the two 

 great median bundles with inter- 

 jacent compact mechanic tissue. 

 The lateral bundles are usually re- 

 duced in number, more rarely 2 — 3 on 

 either side (shaUow-water form from 

 Hokianga, below! and pp. 169, 176!). 

 The length of the peduncles and 

 the upper internodes varies consider- 

 ably. In the main-form, of St. 

 John's Lake, the petioles of the 

 primary involucral leaves are of 

 equal length to the blades and those 

 of the leaves next below likewise 

 comparatively short. Specimens from 

 Nelson (see below!) have rather 

 elongate internodes (10 — 17 cm) next below the primary spike and the petioles of 

 the primary involucral leave likewise elongate (9 — 10 cm). I have called such specimens: 

 f. corymlboides n. f. — F. foliis flor. prim, longissime petiolatis, internodiis 

 superioribus valde elongatis. — 



The specimens from Hokianga evidently are a shallow-water form with a couple 

 of branches at the base, short internodes and only coriaceous leaves: 

 f. frondosus n. f. — F. foliis omnibus coriaceis v. subcoriaceis. — 

 The specimens from Tasmania, again, have sessile or very short-petioled sub- 

 mersed leaves and reduced faculty of developing coriaceous leaves. Besides, this 

 form entirely lacks the interlacunar circle of bundles, whereas the subepidermal one 

 is well supplied. This plant I name: 



f. tasinaiiicus n. f. — Folia submersa sessilia vel insuperiore parte caulis brevi- 

 petiolata, omnia obtusa, basi lanceolata; natantia sero evoluta parva ovalia. — 

 Fig. 91, E—H. 



Fig. 91, P. Cheesemanii Benn. A — ■/>, typical form. A, Involucral 

 leaf, {. B, Top of a submersed leaf, f (from Lake Pearson). C, Pistil, 

 sideview, \^ (from St. Johns Lake). D, Transverse section of the stele, 

 a — a, median bundles; ft, bast; c, lateral bundles, \". — E — H, form 

 tasmanicas Hagstb. E, Involucral leaf, -}. JP, Top of a submersed leaf, 

 f. G, Pistil, lateral view (a), from above (6), 'y". H, Diagrammatic cross- 

 section of the stem, showing the central stele (identic with that of the 

 typ. form) and the subepidermal strands, Y- 



