. Critical researches on the potamogetons. KUNGL. SV. VET. AKADEMIBNS HANDLINGAE. BAND 55. N:0 5. 213 species respecting the interlacunar cortical bundles which often occur in two circles or in one complete ligular circle and one incomplete one within it, whereas P. gra- mineus always has only one (the ligular) and P. lucens always (2—) 3. Subepider- mally there are scattered strands. The endodermis- cells sometimes present the liicens-type, sometimes the more compressed type characteristic of P. gra- 7nineus. The arrangement of the central bundles corresponds with that of the two parent-speci
. Critical researches on the potamogetons. KUNGL. SV. VET. AKADEMIBNS HANDLINGAE. BAND 55. N:0 5. 213 species respecting the interlacunar cortical bundles which often occur in two circles or in one complete ligular circle and one incomplete one within it, whereas P. gra- mineus always has only one (the ligular) and P. lucens always (2—) 3. Subepider- mally there are scattered strands. The endodermis- cells sometimes present the liicens-type, sometimes the more compressed type characteristic of P. gra- 7nineus. The arrangement of the central bundles corresponds with that of the two parent-species. In order to get a synopsis of the many forms, the Fiberian arrangement of the year 1838 can still be maintained with the closer definition I have made in Neuman, Sveriges Flora, 1901, 796. It is namely apparent that the middle internodes of every form has a tendency to elongate themselves, whereas the upper ones seem to present more con- stancy. Var. a validus Fieber : Internodia omnia aut saltem superiora tiia sub spica primaria breviora, 30—60 mm, vel infra. Folia suprema interdum na- tantia vel subcoriacea. To this form-series ought to be reckoned: f. Iiicescens (Tis.) Hagstk. P. lucens p luce- scens Tis., 1. c. no. 59: — Folia caulina magna, 20—25 mm lata, omnia breviter petiolata. Stipulaj breviores et magis quam in P. lucente caducse. This form passes over into f. foliosus which, however, has longer internodes and nearly sessile and still larger stem-leaves. The ligules always show influence from P. gramineus. f. longipetiolatus (Tis.) Hagstr. P. hicens 7 longipetiolatus Tis. 1. c. no. 60, non no. 144: — Folia superiora longe petiolata. Ligulce magis per- sistentes. Leaves as in the precedent, but at (under and over) the primary spike (in the stem-elongation) long-petioled (influence from P. gramineus), petioles never longer than the blades, though, usually shor- ter. Ligules longer persistent, i. e. more hicens-like. The topmost leaves sometimes have nearly
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