429 



In Greenland the habitats are grassy slopes, copses and 

 luxuriant heaths (Rosenvinge, (I). 



Geographical Distribution. West Greenland (com- 

 mon south of Godthaab), Labrador. Canada, Unalaschka, Kamt- 

 chatka, Arctic Siberia (Lange, Rosenvinge, (I). 



Anatomy. (Compare \L\rie 1. c). The epidermis of the 

 root of the first order is more or less collapsed and corky 

 and bears root-hairs ; the exodermis has somewhat thickened 

 walls in which the middle lamella is suberized. The cortex is 

 from 4 to 6 layers thick, the cells are somewhat collenchy- 

 matous and the intercellular spaces very small. The endodermis 

 has somewhat thickened, suberized walls; the pericycle is one- 

 layered. The central cylinder is diarch, the vessels filling up 

 the greater part of it; the two groups of sieve-tissue are 

 diametrically opposed to each other and are surrounded by 

 wood-vessels upon the three sides. In the roots of the 

 second order the cortex consists of about three layers; the 

 innermost layer is of large, radially elongated cells, the outer- 

 most has somewhat coUencliymatously thickened walls. The 

 epidermis has a tendency to collapse, it may however bear 

 numerous root-hairs. The groups of wood in the diarch central 

 cylinder are not fused together. The cortical cells in these 

 roots contain hyphae which form balls in them. 



Regarded anatomically there is a difference between the 

 vertical and the horizontal part of the rhizome, in that the 

 former has a phellogen which, according to Marié, develops 

 from 3 or 4 outer layers of the cortex. The cork is 3 — 5 

 layers thick. The horizontal rhizome, on the other hand, 

 retains its small-celled epidermis which has arching and fairly 

 thick outer walls. The cortex is almost similar in both parts 

 of the rhizome and is rather compactly built of cylindrical cells 

 which, especially in the vertical part, are rich in starch. The 

 starch-grains are either single or compound. In the horizontal 

 part of the rhizome there is a continuous wood-ring ; the 



XXXVI. oc 



