108 



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



labelled »Herb. of the U. S. North Pacific Exploring Expedition under Commanders 

 Ringgold and Rodgers 1853 — 56. C. Wright coll. Loo-Choo Islands*. They are 

 determined by Maximowicz himself as limosellifolkis. 



In habit and in most qualities it is like a small P. panormitanus. Regel in 

 Fl. Ussur. plainly calls it P. pusillus. 



The stem is thread-like, terete or but faintly compressed and to the inner struc- 

 ture corresponding with the usual type of the group. The subepidermal strands are 

 very faint; no pseudo-hypoderma; central cylinder of the circular diagram type. 



Leaves three-nerved, stem leaves 20—30 mm long, scarcely 1 mm broad, base 

 tapering, apex with a short cusp; a narrow channel on either side of the small lacunae 

 round the midvein (I — I), no strands are observed in the lacunar system. Accord- 

 ingly P. limoselUfoUus is a non-sclerenchymatous species. The involucral leaves are 



semicoriaceous in close correspondence with P. panormitanus. 

 Blade and petiole more or less distinctly differentiated; blade 

 without stomata, not fully 2 mm broad. Ligules 8-fibrous con- 

 nate as in P. panormitanus. 



The spike consists of only two verticils. Style short, stigma 

 almost oval covering the whole upper surface of the style and 

 projecting a little beyond. The fruit lacks a dorsal keel and 

 outgrowths according to the outline of it made by Maximowicz 

 on the label, and is somewhat like a panormitamis-hmt, but 

 shows no affinity with the Javanici. No turios are seen by me. 



A/ 



C: 



1 



Fig. 43. P. ItnioseUifuIlus 

 Maxim. A, Top of sabmersed 

 leaf showing the nervation and 

 the form of the cusp, f. B, 

 Two involacral leaves {« — b) 

 &, more conspicuously diffe- 

 rentiated, {-. C, Transverse 

 section of a submersed leaf, 

 i-J", see the text! D, Pistil, 

 side-view, f. 



Series B. Pusilli COnvoIuti Hagstr. 

 Subseries a. Acuti Hagstr. 



All the species of this subseries have a distinct, sharp 

 cusp, or a slowly tapering point. I do not know more than 

 the following seven species and hybrids: P. Hillii, P. Gayii, 

 P. Berteroanus and P. Aschersonii, belonging to North and South America, P. orien- 

 talis a native of East Asia, and P. Preussii, of Africa. A South-American hybrid 

 shows evident relationship to P. Aschersonii and polygonus. 



P. Hillii MoRONG. 



In Botanical Gazette 1881, 290, — Fig. 44. 



Stem flattened and furrowed at least on one side, 2,5 times as broad as thick, 

 and of the typical structure ; stele diagram oblong. Epidermis-cells of elongated form, 

 3 to 5 times as long as broad; a pseudo-hypoderma lacking in the stem is present 

 in the peduncle, where, again, the sclerenchymatous strands are absent. The vas- 

 cular bundles of the latter run very near together reminding in that circumstance of 



