42 



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



clr 



also has the same curvature, but in dried state false keels are often formed both 



dorsally and laterally. 



The epidermis-cells of the stem always consist of long narrow cells which here, as 



in all the Coleogeton-species, increase somewhat in length in the peduncle. The pseudo- 



hypoderma usually consists of a 

 two-celled layer in the basal in- 

 ternodes, in the upper ones it is 

 one-celled. Interlacunarly there 

 always occurs the vaginal circle 

 of more (basally) or fewer (up- 

 wards) vascular and fibrons bund- 

 les. In most cases there are at 

 the middle of the stem 6 — 12 

 bnndles, and in the top internode 

 as a rule 4 bundles. In the ped- 

 uncle, on the other hand, they 

 are without exception absent. 

 The endodermis of spike-bearing 

 specimens always consists of well 

 developed M-cells of the broad 

 type. Crosscut-form of the stele 

 oblong at the base of the stem, 

 more roundish or circular in the 

 top, fig. 16, A, B, C. The bund- 

 les of the stele are arranged in to 

 three groups as usual, the median 

 one with two separate bundles 

 (basally), thus four-bundledly, or 

 two fused bundles (upwards), the 

 oblong type. In the top of t lie 

 stem and especially in the ped- 

 uncle, the laterally situated bund- 

 les grow more rcduced and often 



Fig. lfi. /'. peetinatut L, A, Ii, C. Aiiatomioal diagram of tho central 

 cylinder, diffi-n-ut mdividuals, serving to show tho ohief typea of tho arrange- 

 nient of bundles and channcls, ca. 6 ,°; A, from tho basal part, four-bundled. 

 Ii, from the middle of tho stem, oblong type, C, from the appermost inter- 

 Qodi next to the peduncle, more enlargod, oblong type compressed; letters 

 as in lig. I. I) — II, Transverso sections of leaves showmg tho arrangemenl 

 of norves and tho lacnnar system of leaves of different width; /', Leaf of 

 abort i 'i mm In width; £7, Leaf of var. toitoraetu» (V v..), "•■■. F, Btem-leaf seem to be groiipcd 1'Olind a COIU 



of var. ttriatUi (B, >t 1'.), from Jujuy and Pndagael, B Aniirir.i. and I 



broadleaved Bpecimeo from Trendå in Danmark, ",''; O, Narrowor leaf, : 1 "; 

 //. rar, mongolieu» Bknm., Bpidermia without pseadohypoderma, *f. Letters, 



see tho text! 



mon xylem cavity (circular dia- 

 gram-type). In the rachis the 

 four bundles again run separa- 

 tely, the four-bundled type having thus returned. 



The leaves usually present three vascular bundles, m, n l fig. 16, D, E, 0; and 

 the luteral bundles run considerably nearer to the börder than to the Blid r ib. Broad 

 leaves eontain two pairs of lateral ncrves arranged as is shown in the fig. 16, /•'. n\ 

 n 2 . A rcduced condit ion, again, is to be found in extremely narn»w leaves, fig. 16, //. 

 Subepidermally there occurs nearly always at the margin a weak bast-bundle which 



