377 



cortex are collenchymatously thickened, but only in roots of 

 the first order. The cortex acquires at an early stage large, 

 lysigenous lacunae. The endodermis is suberized, but the walls 

 are not thickened. The central cylinder is di- or triarch in 

 roots of the first order and diarch in roots of the second 

 order. The latter contain hyphæ which are usually found 

 rolled together into balls in the inner layers of the cortex 

 Fig. 25, 6'); such mycorrhizas have been found in specimens 

 from Disco, Kaafjord and Spitzbergen. 



The rhizome is similar to that of R. glacialis. 



The stem above ground nearly resembles in structure 



Fig. 25. R. nivalis. 



A, Transverse section of adventitious root of the first order (Disco; about ^"/i). B. Por- 

 tion of A (about ''"/i). C, Mycorrhiza of root of the second order (Kaafjord; on/i). j)^ 

 Transverse section of peduncle (Spitzbergen; 6, 8. 1910; about 1*^/1). b, Bast; c, cortex; 

 end, endodermis; ep. epidermis; ex, exodermis; Л, hyphæ; I, lacuna; m, pith; mh, pith- 

 cavity; p, non-lignified parenchyma; ph, leptome; vp, lignified parenchyma; x, xylem. 



that of R. sulphureus. The cuticle is more slightly striped 

 than in the latter. The stomata are on a level with the sur- 

 face. The epidermis contains chlorophyll and is attached to 

 the outermost layer of the cortex ; the rest of the lacunose 

 cortex, extending inwards to the ring of stereom, is about five 

 layers thick. The development of the stereom is about equal 

 to that in R. sulphureus; this applies also to the fibrous tissue 

 outside the leptome. The peduncle, as usual, is considerably 

 stronger towards the time for the ripening of the fruit than 

 at an ealier stage (Fig. 26, D), and it is somewhat stronger in 

 R. nivalis than in R. sidphureus: in the former it is also more 

 strongly furrowed. Consequently, judging from my material. 



