442 Fr. J. Mathiesen. 



and 69° 30' N. lat. (Rosenvinge, 1892), on the whole rather 

 rare there; Labrador, the Rocky Mountains, the continent of 

 Arctic America, (but not mentioned by Simmons from the 

 Archipelago), Siberia and Dahuria. 



In Greenland it grows on luxuriant, damp heaths; the 

 species requires a snow-covering during its winter-rest (M. 

 PORSILD, 1920). 



Anatomy. The root is of the type described later on 

 in P. hirsuta and lanata and, as in these, the secondary 

 cortex is traversed by numerous radial clefts. There is, how- 

 ever, a difference between P. euphrasioides and the two spe- 

 cies in question as regards the nature of the xylem-part, 

 because, in the two former it is composed of a large quantity 

 of non-lignified tissue and of relatively few vessels only, 

 whilst in P. euphrasioides one always finds in the root several 

 concentric rings, each consisting of numerous vessels with 

 intervening lignified stereom (thin-walled wood-fibres). 

 These continuous rings of lignified elements, the outlines of 

 which are however somewhat undulating, are separated by 

 portions in which the vessels are not so wide or numerous, 

 and are surrounded by non-lignified tissue; here clefts occur 

 between the radiating lines of vessels. 



That these rings of vessels and wood-fibres really in- 

 dicate zones of annual growths, is evident from the investiga- 

 tion of some specimens chosen from among the individuals 

 in my material, which had flowered for the first time: such 

 as — judging from the leaf-scars — - had had only a vegeta- 

 tive-stage of one-year's duration (that is to say, flowered 

 in the second year) showed two rings; others which, as far 

 as I could see, had had a vegetative-stage of two-year's 

 duration, showed three rings. The greatest number I suc- 

 ceeded in demonstrating amounted to three. 



The cavity of the stem is comparatively large. The 



