KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. NIO 5. 177 



less far down into the internodal portion of the stem. This basal phenomenon has 

 come to pass in the shallow-water form of Domfront. But on the whole it is a very 

 rare event. 



The endodermis-cells are originally O-cells with a tendency to become w-cells 

 at the places where they börder on the bast sheaths of the central bnndles. Close 

 by the nodes the endodermis always has O-cells, as also generally in the portions of 

 it, lying between the bundles. In P. polygonifolius we often find the w-cells very 

 faint, whereas in P. coloratus they are much stronger, in consequence whereof this 

 species never lacks it-cells proper in the internodal parts. 



The leaves are better differentiated in P. polygonifolius than in P. coloratus 

 and the f loating leaves have a greater number of longitudinal nerves, mostly 17 — 19 

 (13 — 23), whereas the number in P. coloratus almost constantly is 15 at the middle 

 of the leaf. The apex of the snbmersed leaves of both species, but especially in P. 

 polygonifolius, is slightly cucullate, by which the} 7 show affinity with P. prcelongus. 

 The species has also a tendency to stretch the petioles and only land-forms have 

 shorter petioles, yet mostly as long as the blade. The colour, especially at the base 

 of the plant and on the fruit has a touch of reddish-brown. The usual measure of 

 the fruit is 2— 2,5 X 1.5 mm. Prof. P. Graebner states (Potamog. 65): »plerumque 3 

 mm» which, of course, is a misprint. Operculum strongly keeled. 



As to the variations, Chamisso and Sciilechtendal have already established 

 two, cordifolius and lancifolius (Linnsea 1827, 215). To this is to be remarked, that 

 the species seems to tend to the subcordate leaf-form, which, therefore, in general is 

 met with when the plant has had occasion to prolong itself by branches of a higher 

 degree (3rd — 4th), even if the primary and the secondary involucral leaves have a 

 lanceolate base. The cordate (subcordate) leaves often get almost straight sides, by 

 which they obtain a very characteristic appearance (Fig. 92, .4). The commonest 

 form is without doubt v. amphibius Fries, to which belong such forms as ericetorum 

 Syme (leaves long-stalked, blade oblong, oval — rounded, 5 X 2.5 cm), Arrhenii 

 Fries (small-leaved as P. parnassifolius, and with a touch of yellow), sphagnophilus 

 Neuman (shorter-petioled, blades of ordinary size and form and shading in yellow). 

 To this var. belongs also a Norwegian form, with short petioles (of about the length 

 of the blade) and broadly lanceolate blades (see fig. 92, BI): 



f. norvegicus n. f. — : Folia elliptico-lanceolata, petiolis lamina sequantibus. — 

 Fig. 92, B. 



Hab. Nonvay, Sogn, 64, Wittrock (hb. Lund.). — 



A form of this species from Madera, S. Anna, 65, Mandon (hb. Stockholm.) 

 is very broad-leaved. I have named.it: 



f. maderensis n. f. — Forma foliis maximis, 70 — 80 X 25 — 50 mm. P. Lesche- 

 naultii Ciiam. & Schl. in Linnaea, 1827, 223? 



This form may be something near f. maximus Fischer. — 



P. parnassifolius, to my opinion properly a small-leaved form of v. lancifolius, 

 has already by Grenier been classed as a variety of this species (Fl. Fr. III, 1855, 

 313). — F. angustifolius Fries and f. largior Tiselius cannot be distinguished from the 



K. Sv. Vet. Akad. Handl. Band 55. N:o 5. 23 



