302 



transitions to the main species. They all seem to me, both the 

 more and less divergent, best regarded as f. litoralis Lindberg 

 (1906 p. 109), which only differs from the main form by somewhat 

 shorter and broader leaves (12— 17 mm long and 2—3 mm broad), 

 usually 6—8 in a whorl (flg. 1); in the Greenland specimens 9 

 may occur, according to Kruuse (1906 p. 224) even 11. The 

 few plants which agree with the description of H. maritima 

 Hellen. (1786), or as Lindberg explains, more correctly H.tetra- 

 phylla L. fil. (1781 p. 81), without however having the characteristic 

 habitus of this, might possibly have developed into f. litoralis^ 

 the lower parts of the stalk of which may sometimes have 

 short, broad leaves at a height of several dm. 



The few specimens I have seen from Finmark, Lapland, 

 Nova Zembla and Waigatsch somewhat resemble the Greenland 

 ones, whereas most of those from Iceland approach more to 

 or are even the typical H. vulgaris, thus 10— 11 -leaved plants 

 from Vallanes, taken in two successive years by Mr. H. Jonsson. 



The rhizome forms a sympodium, the structure of which, 

 so far as the material was able to show, agrees with the de- 

 scriptions in Irmisch (1854 p. 281) and Warming (1884 p. 69). 

 PoRsiLD (1902 p. 206), who gives an account of the occurrence 

 of Hippuris on Disko Island in West Greenland, 69°— 70° N. L., 

 found the rhizomes about 15 cm down in the mud, in as men- 

 tioned 30 — 70 cm of water, the depth preferred by the plant 

 here, especially in clefts between the rock boulders or between 

 loose stones. 



Some plants, among them one found by Jens Vahl "in 

 stagnis sinus Tessarmiut, (= Tasermiut), South Greenland", are 

 richly provided with adventitious roots in the lower leaf-whorls 

 of the upright shoots, like individuals according to Irmisch 

 (1854 p. 287) which grow in damp soil, not in water; yet even 

 in shallow water, which Hippuris is said to like in the polar 

 regions, extensive production of roots may occur. 



In a basin with shallow water in the Botanical Gardens of 



