— 264 — 



apex. Stem with vascular bundles and bast bundles in the bark 

 but without subepidermal bast bundles; 1—2 strata of cells between 

 the epidermis and the outer lacunae. G-endodermis, at least in 

 front of the vascular bundles. The axial cylinder with c. 8—11 

 free, circularly placed vascular bundles (fig. 3 D). 

 P. praelongus Wulf. 



3. P. perfoliatus-groiip. Leaves all thin, broad, sessile and sub- 

 merged with a broad base meeting around the stem; most generally 

 serrulate. Stem without bundles in the bark, or but very rarely 

 with a single or a few small bundles (fig. 4 C, s). Axial cylinder 

 with free vascular bundles (Fig. 3 A). 



P. perfoliatus L. 

 This group is closely allied to the preceeding group, from 

 which it differs by being usually quite without bundles in the bark. 

 Very rarely occur specimens with one or a few small bundles, 

 while P. praelongus is always richly endowed with bark-bundles. 



4. P. crispus-group. Leaves all thin, sessile, serrulate, submerged, 

 with scarious, early perishing stipules. Stem compressed, without 

 bundles in the bark. O-endodermis. Axial cylinder's vascular 

 bundles united in three groups (fig. 3 K). 



P. crispus L. 



5. P. malainus-group. Leaves all thin, not linear, petiolate, sub- 

 merged. Stem with bundles in the bark. G-endodermis. Axial 

 cylinder's vascular bundles free. 



P. malainus Miq., P. sumatranus Miq. 

 Of both these species is said that the leaves are all submerged ; 

 on specimens examined by me, the uppermost leaves seemed to 

 be rather thick and resembled floating leaves; if really floating 

 leaves exist in this group, we shall have to unite it with the P. 

 amplifoUus-gvowp. 



6. P. lucens-group. Leaves mostly thin, serrulate, submerged, 

 but often also floating leaves occur. Stem with bundles in the 

 bark. G-endodermis. Axial cylinder's vascular bundles united in 

 three groups (fig. 3 G—I). 



P. lucens L., P. gramineus L. 

 As elsewhere stated (Raunkiær 1. c, pag. 49 — 50) by P. grami- 

 neus, the vascular bundles of the axial cylinder may be entirely 

 separated; in this case there is no sharp limit to be found between 

 the P. iucens-group and P. amplifolius-group from which then the 



