76 J. O, HAGSTROM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



is the case with several other nearly allied species. One or a couple of subepi- 

 dermal strands can also be perceived in the peduncle. — Epidermis-cells always 

 rather short, usually 2—4 times as long as they are broad. 



The leaves are very narrow (i— I mm) always three-nerved and tapered at 

 the base. Apex acute except in the involucral leaves, of which at least the topmost 

 one usually has a more or less obtuse apex. The lacunar middle portion of the leaf 

 is abundantly endowed with sclerenchyma. Its anatomy as seen in the fig. 29, C. 

 The inner leaves of the iurios hidden by the sheaths are very short, obtuse or round- 

 ish-obtuse, pointless, 7 — 8 in number, the outer or lower ones, 2 — 4 in number, are 

 free, a little protruding, and in the basal part semiterete, by which they differ from 

 the other branch-leaves. 



The ramification of this species is usually very abundant. According to J. Gay 

 very short rudimentary branches grow out from the axils, on which later on the 

 longer branches are formed in an unlimited number as branches of the second rank 

 while the rudimentary branch grows on. Those longer branches, however, are said 

 to be found only on the side of the short branch turning to the stem, in the axils 

 of the 2nd, 4th, 6th etc. leaf, whereas the 1st, 3rd, 5th etc. leaf are said to 

 be barren. This explanation given in 1854 (see Bull. Soc. Bot. France of that year, 

 p. 46 et seq. !) has as late as in 1907 been adopted by P. Geaebner. I cannot 

 join this opinion. The mode of ramification of this species is fuily concording with 

 that of P. vaginatus (vide fig. 11, D, pag. 32!) that is to say the branches are of 

 the first, second, third etc. rank in relation to the main-axis, see also Raunki^b, 

 Danske Blomsterpl. 1896, p. 37—38! 



Another character combining this species with the Coleogeton-S])ec'ies, is that 

 the strongest of the buds of the two involucral leaves is the lower one. Those buds 

 do not, however, come to any rich evolution as for instance in P. jmsilhis, but the 

 spike-production is generally accomplished with the primary spike. Nevertheless the 

 species becomes very rich in spikes since the numerous branches beneath the primary 

 spike are in general spiciferous according to the type C, Fig. 2. This peculiarity 

 gives to the species a characteristic appearance among the other narrow-leaved spe- 

 cies, corresponding to the state or aspect of P. vaginatus within the subgenus 

 Coleogeton. 



The species does not vary considerably. Some authors have distinguished 

 varieties with three-nerved leaves, but the leaves are on closer examination always 

 three-nerved. Such varieties as Trimmeri Gasp, and capillaris Fischer, recorded as 

 three-nerved and by this fact separated from the main-form, are probably bastards. 

 The species has, namely, a formerly not sufficiently observed tendency of crossing 

 with a great many species, by which fact many aberrant forms get a satisfactory 

 explanation. 



The fruit, however, varies as to the development of bosses or protuberances 

 the producing of which P. irich. is much inclined to. This pecularity has, however, 

 not any great systematic importance, as the same individual often shows fruits with 

 an appearance different in this respect. Chamisso's description evidently refers to 



