301 



than 30 cm depth, "liable to drying up", Porsild (1902 p. 206), 

 however also in deeper water, 30— 70 cm. In "Norges arctiske 

 flora" it is stated, that "it grows most often in localities, where 

 in the earlier part of the summer it lives in water and towards 

 autumn in the air" iNorman 1895 p. 2781. 



With regard to ils growth at Disko, West Greenland ca. 

 70° N. L., Mr. Porsild has given me the following information. 



^'■Hippuris grows preferably in small pools, small depres- 

 sions in gneiss, often for example no larger than a large bath, 

 so long as they contain water through the whole summer. 1 

 have only seen it quite dry once, in the very dry summer of 

 1909, in a small lake on sandy bottom. It lay there in a curious 

 tangle, but living, with flowers and fruit, and covered the whole 

 bottom. 



In larger lakes it forms the outermost belt of the vegetation, 

 outside the Carex-Equisetum belt. As there is a predominant 

 wind-direction at each single place, and as this determines the 

 mode of growth, we always find the marsh plants and Hippuris 

 on the sheltered side, whilst as a rule there are no plants on 

 the windward side. The seed namely is carried over to the lee side, 

 loose parts of the plants are washed over here, and here there 

 is a "gytje" of dead material of Nostoc, of submerged, growing 

 Hypnum species and the like, and in this grow Hippuris^ 

 Batrachium, Callitriche and Potamogeton. The fairly dark 

 material and the dark mosses (e. g. H. scorpioides) absorb con- 

 siderable quantities of heat, and the water is here always much 

 warmer (up to 12° — 15° C.) than on the windy side over naked 

 bottom. 



In lakes and lagoons with a little brackish water I have 

 never seen Hippuris". 



According to Lange (1880 p. 13 and 1887 p. 237) and several 

 later authors, the true H. vulgaris occurs very seldom in Greenland 

 and most Greenland specimens are referred to v. maritima Hartm. 

 <== H. maritima Hellen,), though, it is added at several places, with 



XXXVI. 20 



