34 J. O. HAGSTKOM, CRITICAL EESEARCHES ON THE POTAMOGETONS. 



Besides, the turios differ from those of P. pectinatus while they as to their 

 nature are congruent with those of P. filiformis. 



Late in autumn they are formed at the end of the rhizome (fig. 11, E, a) 

 and consist of the 3 (or 2) last generations (I, II, III) of it together with their 

 shoots in bud-state. The third and fourth internodes of the generation I swell to 

 an oblong form, and the four first ones of // likewise. 



In the meantime a concrection takes place just as in P. filiformis and the 

 whole turio holds a length of about 4 — 5 cm (cfr. Hagstrom, Potamog. in Neu- 

 MAN, Sveriges Fl. 1901, 793, where we have the very first mention of these buds). 

 C. W. FoNTELL, in his researches, has happened to find a locality, where the species 

 is vegetating throughout the winter, and from this he has precipitately drawn the 

 conclusion, that no winter-buds are to be found : — Eigentliche Winterknospen finden 

 sich nicht (Beitrage etc. 1909, 15). 



I have never observed that in this species the stem elongates itself with spi- 

 ciferous branches from the base of the peduncle, as often does P. pectinatus. Other- 

 wise the spiciferous branches are arranged after the type C, Fig. 2. Concerning the 

 ramification I refer to the figure 11, D. 



Anatomy of the stem: Epidermis-cells very short, nearly cubic; inside the epi- 

 dermis there is a layer of 1 — 2 cells and 5 — 6 (7) circles of lacunae, the larger ones 

 outward, the narrower inward. Nearest to epidermis a few small cells are also met 

 with alternating with the larger ones. In the cortex occur, dependent upon the 

 height on the plant at which the cuts are placed, five (basal part) or four (the 

 middle) circles of numerous vascular- and bast-bundles, by which the stem becomes 

 very strong and tough, able to support the abundant growth of branches. In an 

 individual of medium size the author has, in a section from the middle part of the 

 stem, counted 60 such strands, of which 40 — 45 evidently possess no vessels and 

 only serve as mechanical tissue. The endodermis consists of strong it-cells of the 

 common broad type and is, moreover, on the inner side strengthened by a layer of 

 bast-cells. The vascular bundles of the stele are disposed after the eight-bundled type 

 in three groups, a median one with two bundles, and two lateral ones with three more 

 or less conspicuous bundles each. The median bundles form one air-channel each, 

 laterally there are at least two wide channels, sometimes even more, and in the basal 

 internodes usually eight. The cells of the pith often have thickened walls and 

 the bundles are always surrounded by mechanical celles (bast-sheaths). 



The central axis of the peduncle has the same structure as that of the middle 

 or upper internodes of the leafy shoot, and in the peduncle there is also to be ob- 

 served a circle of cortical strands, so far as known not met with in any other spe- 

 cies of the subgenus. P. vag. accordingly proves to be a genuine sclerenchymatous 

 species, whereas P. filiform,is is a non-sclerenchymatous plant. 



A leaf in cross-section presents a lacunar system chiefly in accordance with 

 that of P. pectinatus and exhibiting more or less complicated variations correspond- 

 ing to the width and thickness of the blade. Peculiar to this species is that the 

 lateral nerves (fig. 12, E, «') run at a considerable distance from the border. Be- 



