389 



two weeks), but the majority of them sink within 48 hours if 

 the surface gets wet (according to my experiments, made with 

 Danish fruits^). I can make no statement about the germination, 

 but the fruits of the nearly allied E. Flammula are capable of 

 germinating immediately after maturation. 



R. reptans grows on the pebbly shores of lakes, where it 

 often forms a dense mat; it may also occur among moss 

 (Hartz); it is often submerged and the leaves are then linear 

 and it is sterile; Norman records that in Arctic Norway it may 

 be found in large expanses of water at a depth of as much 

 as one metre. According to Norman it is a decidedly continental 

 plant in Arctic Norway in the greatest contrast to R. Flammula. 



Geographical Distribution. North America, from 

 Canada and Newfoundland to 69°N. lat. ; West Greenland; Ice- 

 land; the Færøes; Central Europe; Scandinavia, as far as Fin- 

 mark; Finland and Arctic Russia. (Lange). 



Anatomy. The root resembles in structure that of other 

 species of Ranunculus. Roots containing reserve food-materiai 

 (of which only Danish specimens have been investigated) have 

 a still entire epidermis; the exodermis is of somewhat radially 

 elongated cells with undulating walls; both the layers are su- 

 berized. The cortex has no thickened outer layers; its cells are 

 full of starch (the grains are compound). The endodermis is 

 suberized but the walls are not thickened. The central cylinder 

 is diarch, the vessels are slightly developed. The slender roots 

 have a more or less collapsed epidermis and the cortex is for 

 the greater part broken down. The central cylinder is also diarch 

 in these roots. The diameter of the central cylinder relative 

 to that of the root is only slightly smaller in the roots containing 

 reserve food-material than it is in the slender ones. 



Mycorrhizas have not been found. 



The nodes and the internodes of the stem differ some- 



^ See also Kølpin Ravn: Om Fhdeevnen hos Froene af vore Vand- og 

 Sumpplanter. Bot. Tidsskrift, Bd. 19, København, p. 146. 



