26 J. O. HAOSTEOM, CRITICAL RESEARCHES ON THE POTAMOGETONS. 



P. strictus Phil. Florula atacamensis, 1860, 50. 



P. aulacophyllus ScnvMA^N in Fl, brasil. III. 3, 1894, 696. — Fig. 7, A—B. 



Tliis species also comes very near to P. filiformis. As to style, stigma and 

 ripe fruit it may hardly be discerned from it. The way of brandling, likewise, is 

 also the same: every sheath embraces but one branch. 



The low-grown form, being only 9 — 13 cm high, is to be considered as main- 

 form. It has comparatively short (3 — 6 cm) leaves and short sheaths. Leaves usu- 



Fig. 7. A — B, P. strictus Phil., C — D, P. siricttis Phil. T.ar. mttgellaniciis Hagstb. A, Apex of a stem-leaf, Y. 'te bottoms 

 and walls of the lacunie visible. B, Transverse section of a stem-leaf (middle part), a, vascular bundle of the midrib, h, lateral 

 bundles, "y". D, apex of a stem-leaf of v. mcigell., 'j", bottoms and walls of the lacunra visible. C, Transverse section of a stem- 

 leaf, middle part, a, and b, as in B, ski, marginal bastbnndles, y". 



ally a little over 1 mm broad, of the same width up to the rounded apex, canali- 

 culate and obtusely keeled, 3-nerved, the lateral nerves being a little more removed 

 from the margin than in P. filiformis. Ligules truncate or subretuse. A cross- 

 section of the leaf presents very seldom a faint subepidermal strand which, again, 

 always is to be found in the variety described below. The peduncles are short, 

 2,6 — 4 ( — 6 — 7) cm, also the spikes that consist of 3 — 4 approximated verticils. 



Anatomy of stem: The Philippian specimens of Atacama exhibit the following 

 peculiarities: Epidermis of long narrow cells, inside strengthened by an one-celled 

 pseudo-hypoderma along which appears a circle of large-roomed lacunae, evidently 

 wider thanin P. filiformis, whereon follow 2—3 circles of narrower lacunae. Three 



