90 



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



one. The subepidermal strands of the stem are lacking in the peduncle but a one- 

 celled pseudo-hypoderma has supplied their place to stiffen the organ. 



The middle part of the stem-leaf is arranged as in the cognates with a promi- 

 nent midrib possessing only one greater air-channel at the side of the narroAver la- 

 cunae. The sclerenchymatous strands are numerous and the marginal bast-bundle is 

 usually strong. The leaf-base generally tapers more slowly than the apex, that is 



acute with more or less inconspicuous cusp. 

 The side-nerves join the midrib at a distance 

 from the very point of 1 — 2 times the leaf- 

 width. In broad leaves a pair of marginal 

 side-nerves occur, which join the main lateral 

 nerves a good bit of way below the point. 

 The nodes of this species lack the oil-cells often 

 occurring in others. 



The styles and stigmas correspond with 

 those of P. pusillus and others with an incon- 

 spicuous style and a low rounded stigma ex- 

 panding over the whole top surface of the 

 style and its border. 



The characteristics of this species are the 

 short peduncles and the few-flowered spikes. 

 The latter usually consist of two closely placed 

 verticils with two flowers in each, forming a 

 little clew. The statement on var. californicus 

 MoR. that it sometimes has »as many as 12 

 roundish fruits* must not be understood as if 

 the spike were to contain 12 flowers. I have 

 seen the Parish's specimens underlying the 

 Fig. 35. p. foiiosus baf. A, A leaf of the broadest Morougian dcscription, and they have no more 

 ^^ ^;:^'fol,tV'^:Ss;isetJ;:?:f:l:::i flowers in the spikes than has the species in 



rower 3-nen-ed leaf, X indicates the places of sometimes preneral. SinCC Cach flower haS four mcricarpS, 



occurring strands (w, n', sir, as nsnal), ^f". D, Trans- ^ ■*■ 



verse section of pednncle. In the centrum foar vascular 12 fruitS mean three floWCrS, Or 4 floWCrS, 



bundles, fused into a common bundle with a common .„ , j-ji'j-iii 



xylem cavity (x), end, endodermis, I, lacunar .system, S". II WC SUppOSC SOmCOUe Or Other Ot tilB piStllS tO DC 



E, Pistil and F, fruit, showing the broadest and narrowest „V,ortivA n« i<s nffpn rvr mr>«flir tVif> fnpt niiarnp- 



form of the keel (the dotted line), i. G, Transverse sect. aOOrtlVC aS IS OltCn Or lUOStiy tUe laCt. UnaraC- 



of liguie, Y. '<; front field, ,-, ridges. tcristic to the specics is further the crested dorsal 



keel of the fruit. The height of the keel or crest varies considerably within the same 

 spike (see the fig. 35, F, where the dotted line signifies the reduced keel). Another 

 peculiarity of the species is the propensity of prolonging the stem by long branches 

 from the base of the primary spike according to the type D, Fig. 2. I have measured 

 such a spike-bearing branch of the first rank on a specimen and its length amounted 

 to 40 cm. It bore no less than 17 leaves from the base up to the spike. The branches 

 of the first rank, in their turn, will bear branches of the second etc. rank. This 

 mode of branching closely corresponds to that of P. pusillus. P. foliosus also corre- 



