- 268 — 



bast bundles. Stem generally with bundles in the bark. Axial 

 cylinder's vascular bundles united in three or in only one group. 

 P. pectinatus L. P. filiformis Pers. 



- puncifolius Kern. - vaginatus Turcz. 



- striatus Ruiz et Pav. - latifolius (Robbins). 

 ? - tenuifolius H. B. R. 



16. P. pusillus-group. Leaves all thin, linear, sheathless, sub- 

 merged, with 1—5 nerves of vascular bundles, without bast bundles 

 except along the midrib and the edge (fig. 6 A — B). Stem terete — 

 compressed with a circle of subepidermal bast bundles but other- 





rs 





sn 2 



àn, 





A 





Fig. 6. A, P. mucronatus (not P. pusillus as said in my book, 1. c. p. 57); 

 transverse section of the leaf (c 65:1). — B, P. trichoides (c. 65:1); trans- 

 verse section of the leaf. — C, P. pectinatus (c. 15:1); transverse section of 

 the leaf. — lg, lacunae; mn, sn u sn 2 , vascular bundles; s and rs, bast bundles. 



wise without bundles in the bark. Axial cylinder's vascular bundles 

 united in three or in only one group (fig. 1 C). 



P. pusillus L. P. mucronatus Schrad. 



- obtusifolius Merts. et Koch. - rutilus Wolfg. 



- trichoides Cham, et Schlecht. - pauciflorus Pursh. 



- Hillii Morong. 



17. P. confervoides-group. Leaves all thin, linear, sheathless, 

 submerged, with 1 — 3 nerves of vascular-bundles but without bast 

 bundles except in the edge and along the midrib. Stem without 

 bundles in the bark. Axial cylinder's vascular bundles united in 

 only one group. 



P. confervoides Reichenb. 



In the specimen of that species examined by me the sub- 

 epidermal bast-bundles in the bark of the stem were lacking, in 

 consequence of which I have separated the species from the P. 

 pusillus-group. 



