112 



J. O. HAGSTBOM, CRITICAL RESEAECHES ON THE POTAMOGETONS. 



1 i in. broad J 



The species shows no tendency to transform the top-most involucral leaves. 

 The pistil has a short style with, a more or less beak- shaped prolongation 

 above, like P. mucronatus, and the rostrum of the fruit, therefore, presents a charac- 

 teristic hook-formed curvature backwards. The fruit-flesh or epicarp is very thin 

 causing the fruit to exhibit lateral pits. This may, however, be an accidental feature. 

 The size of the fruit is recorded to be very considerable (Bennett: s2i lines by 

 Graebner: »fructus 4,5 mm longi, 3 mm lati»). Allowing for the 

 misprint (»in.» for lines) I am nevertheless unable to understand 

 how such measures could be arrived at on so small 'pusillus-Yike 

 fruits. 



The specimens from Santiago (see below!) are endowed 

 with turios. They consist of somewhat swollen tops of branches 

 or short branches, 25 mm long, the lower free leaves of which 

 are considerably reduced in size, spreading and scarcely overreach- 

 ing the obtuse inner ones, clasped by sheaths of equal length. 

 Distribution . South America. Chile, St. Jago?, Philippi 

 (hb. Stockholm.); Brazil, Rio de Janeiro, Glaziou (hb. Stock- 

 holm.); Uruguay, Montevideo, 79, Arechavaleta. Probably it 

 does not transgress the 35° S. L. N. America, Canada, New 

 Foundland, and Sable Island, Macoun (hb. Haun.). Cuba, 

 Wright, 2305 (hb. Stockholm.). 



The above mentioned gigantic form is gathered by P. 

 DusEN in Parana: mouth-district of Rio Cubatao (brackish wa- 

 ter), Vi 1912 (hb. Stockholm.). I have named it: 



f. pusilloides n. f. — Caulis valde elongatus metralis, com- 

 pressus, internodiis ca. 10 cm longis. Foliis majoribus, 90 — 120 

 X 2 — 3 mm, flexilioribus lis P. pusilli simillimis. 



One could almost expect the mechanical tissue to be more 

 richly or strongly developed than usually is the case, but we 

 find no tendency to this, rather to the contrary. 



Fig. 47. P. Asclwrsonli 

 Ae. Bennett A, Top of a stem- 

 leaf, ■^. iJ, Transverse sec- 

 tion ttirough tlie lacanar part 

 of a stem-leaf at the middle, 

 '-f," m, midyein, str, bast- 

 "bundles. C, Transverse sec- 

 tion of the peduncle, str, 

 bast-bundles, Y'- -D, Pistil, 

 side view, \''. E, Fruit, side 

 view, T. 



P. attenuatus n. (spec v.) hybr. 



(P. Aschersonii Ar. Benn. x polygonus Ch. & Schl.). 

 Caulis c. 0,5 m altus subcompressus, simplex vel ramulo- 

 sus, ab axillis foliorum floralium prolongatus ramulis primes — secundse ordinis, inter- 

 nodiis 20—30 mm longis. Folia rigida linearia apice sensim attenuata, modo P. poly- 

 goni, acuta, in superiore parte trinervia, infra medium ut plurimum 5 — 7-nervia; 

 costa media reticulosa; fasciculi libriformes mechanici mediani et marginales validi 

 fere ut in P. polygono. Ligulce cito putrescentes, 10 — 12 mm longse, in parte media 

 6— 7-nervi8e. Pedunculus subteres, 20—30 mm longus. Spica 3—4 verticillata. Pistil- 

 lura stigmate oblongo. — Fig. 48. 



In all specimens here available the pollen is quite sterile. In the vegetative 



