358 



Sylvén is of opinion that R. acer usually germinates in 

 spring, but under cultivation the fruits will germinate imme- 

 diately after maturation, and in Denmark I have observed young 

 germinating plants in August. In the plants which germinate 

 in spring the primary root of the seedling and also the hypo- 

 cotyl live only the first summer, and adventitious roots are 

 developed early from the base of the epicotyl. The sheaths 

 of the cotyledons are slightly coherent (Sylvén, Lubbock, 1892). 



In Arctic Norway the frequency of occurrence of this 

 species is similar from sea-level to high up in the mountains, 

 with local accumulations in the cultivated home-fields and on 

 the snow-line ; in the latter place it often occurs as f. pwnilus, 

 (Norman). In Iceland also it is common in cultivated meadows, 

 a fact which is perhaps to be connected with its above-men- 

 tioned dispersal by cattle. In South Greenland it is common on 

 grass-land, grassy slopes and in willow-copses in the exterior 

 of the country (Rosenv., III). In northern Sweden it grows on 

 damp ground (Cleve), and in Nova Zembla it occurs on the 

 tundra on dry, stony ground (f. borealis Trautv.) (Holm). 



Geographical Distribution. Arctic America, Green- 

 land, Iceland, the Færoes, northern and central Europe, the 

 Alps, Caucasus, Arctic Russia, the Urals, north-east Siberia 

 and JNova Zembla. 



Anatomy. In the roots of the first order the outer 

 walls of the epidermis are somewhat thickened, the exodermis 

 is distinctly marked, the cells are radially elongated and the 

 radial walls undulating. Both the epidermis and exodermis are 

 suberized. The cortex is 15 — 17 layers thick and contains 

 starch; the starch-grains are compound. The two subexodermal 

 layers of the cortex are somewhat collenchymatously thickened, 

 the others are thin-walled and collapse more or less according 

 as to whether the plant grows in damp or in dry ground. 

 (Freidenfelt). The endodermis of the mature root is thick- 

 ened and lignified, with Ihin-walled passage-cells opposite 



