KUNGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 55. NIO 5. 



121 



Distribution. North America, »In stagno ad Jamaica Plain, Mass. orient, Leg. 

 C. E. Faxon V 1880. Herb. Tu. Morong» (lib. Stockholm.), of high growth and 

 with dark sheaths or scales at the base like P. confervoides. »Eastern Mass. U. S. A. 

 V* 83, Faxon» (hb. Uppsal.) probably the same locality as the former. »In cursu 

 molario fluente velociter. Ashland, Mass. Leg. T. M. Morong ? e ° 81» (hb. Stockholm), 

 held by Rev. Morong partly for P. pusillus, partly for P. Claytonii (= Nuttallii). 

 In Salt Lake, Anticosti, Que., Canada, 12. 8. 83, J. Macoun (hb. Stockholm.), of 

 low growth, by Macoun labelled P. obtusifolius, by 

 Ar. Bennett »P. pusillus vel Friesii?». 



Forma Novce-AngUce is collected by E. Tuc- 

 kerman jun. in »Nov. Angl. » (hb. Uppsal.), no 

 further statement about the locality. 



The species, thus, seems to be a native of 

 eastern North America. In the American Museums 

 it is probably stored under the name of P. pusillus. 

 A revision of the American pusillus~f orms, there- 

 fore, may give very interesting results. 



P. pusillus L. 



Sp. pl. 1753, 127. — P. Griesebachii Heuf- 

 fel in Verhandl. des Zoolog.-botan. Vereins in 

 Wien, VIII, 1858, 200? — P. Berchtoldi Fieb., 

 Die Potamogeta Bohm., 1838, 40—41, saltem pro 

 parte (maxima parte?). — Figs. 24, C, 54, 55. 



Concerning the last quoted name I am con- 

 vinced that it does not represent a form speci- 

 fically separated from P. pusillus. Its chief charac- 

 ters: the light stripes along the midrib and the 

 position of the lateral nerves (nearer to the börder 

 than to the main rib) are proprieties exactly charac- 

 teristic to P. pusillus. It is also sure that P. 

 pusillus is sometimes occurring with rather sharp- 

 pointed leaves according to the description of P. 



Berchtoldi. Bat when also described as with larger fruits and broader leaves than 

 those of P. pusillus this plant may answer to the hybrid P. mucronatus X pusillus 

 and I take it for granted that P. Berchtoldi comprehends at least two separated 

 forms, by Fieber confounded with each other. 



The slem of this species is very little compressed. Its anatomy coincides with 

 that of the type: epidermis, subepidermal strands, lacunar system, and a central 

 stele of the circular diagram type. Of P. Berchtoldi I have seen specimens from 

 the very locus classicus »Landskron Bohemia» determined by Fieber himself. They 



Fig. 53. P. lacunatus Hagstb. A, Base (a) 

 and /<, top of a stem-leaf, \ u . B, Top of a branch- 

 leaf, 1 1 °. ^'> Pistil, a, from the side, b, ventral 

 view, *f. D, Frait of the f. Novce-Angliw, from 

 the side, j. E, Transverse section of stem. All 

 bundles of the central cylinder fused iuto a com- 

 posite bundle with a single xylem channel, '^ ; 

 F, Transverse section of a stem-leaf below the 

 niiddle, m, midrib, n', lateral nerves, str, marginal 

 strand, X occasionally occurring strands, 4*. 



K. Sv. Vot. Akad. Handl. Band 55. N:o 5. 



16 



