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



pistil unknown. Fruit extremely characteristic, with well-developed distinctly inward- 

 turned, acute rostrum, convexe sides, and rounded back without keel, 3,5 mm long 

 and 2 mm broad. 



The transverse-section of a leaf shows a structure nearly quite the same as in 

 P. filiformis. The lateral nerves run subepidermally. The bottoms of the lacunae 

 appear to the naked eye as » cross-nerves j (venis crassiusculis transversis: Mey.). 

 The stem-anatomy scarcely exhibits any difference from P. filiformis. The cortical 

 parenchyma has two strands or vascular bundles, the endodermis consists of tt-cells, 

 bundles of the central cylinder arranged filiformis-like in 2 — 4 areas with the same 

 number of cavities. But if anatomically scarcely separated from P. filiformis, it 

 easily differs from this and allied forms by the mode of branching, the very short 

 internodes of the branches, the subretuse ligules, and the fruit. Probably because 

 of the rostrated fruit Meyer says, !>proxime ad P. pectinatum accedit^, and Graebnee 

 considers it as proles under that species, whereas Baagoe correctly puts it nearer 

 to P. filiformis, with which the sheaths undoubtedly connect it. In fact P. amblyo- 

 phyllus is a very beautiful and interesting species within this section, analogous with 

 P. pectinatus in the following. 



Distribution. Asia, China borealis prov. Kansu orientalis, 1885, G. N. Pota- 

 NiN (hb. Stockholm.). Thus we have this species from the Caucasus and eastward 

 probably as far as the Pacific. 



The five species treated of above have been found to be both morphologically 

 and in their biological and anatomical conditions nearly allied to each other, and 

 the same can also be said of the species of the next section. 



Sectio 11. ConVOluti Hagstr. 



Folia firmiora, fasciculis libriformibus subepidermalibus non solum in marginibus 

 sed etiam in medio instructa, 3— 5(7)-nervia. Vagince ssepe albido-marginatse semper 

 fissae et in parte inferiore subconvolutae. Fasciculi caulini libriformes corticales 

 numerosi, praesertim in inferiore caulis parte. Pollinatio in superficie, ut videtur, 

 aquae fit. 



All the species belonging hereto are rich in sclerenchymatous tissue and endowed 

 with open leaf-sheaths, which are subconvolute. They should be described under two 

 subsections with regard chiefly to the fruit. 



Subsectio 3. Vaginati Hagstr. 

 Fructus rostro humili verrucseformi. 



P. subretiisus n. sp. 



Rhizoma gracile. Caulis badeus filiformis tenuissimus teres elatus, internodiis 

 inferioribus brevibus, sequentibus sensim longioribus, summo pedunculi fere longitu- 



