359 



to the 4 — 5 radial masses of wood of the central cylinder. 

 According to Freidenfelt the cambium can develop in older 

 roots some secondary wood. The leptome-mass has the usual 

 large pentagonal tube which is wedged in between adjacent 

 cells of the pericycle. 



The roots of the second order have an exodermis and 

 endodermis like those mentioned above; all the layers of the 

 cortex (about 4) are thin-walled, also the endodermis, which is 

 corky. The central cylinder is diarch. Schlicht has found 

 endotrophic mycorrhizas in the lower part of the primary root 

 and in roots of the second order. The specimens from Den- 

 mark, the Faeroes and Iceland which I investigated also had 

 mycorrhizas in the above-mentioned parts of the roots. The 

 hyphæ were often rolled together into compact balls in the 

 inner layers of the cortex. Roots from Greenland have not been 

 investigated. 



The rhizome. (Compare Hj. Nilsson), in the specimens 

 investigated, the epidermis was, for the most part, collapsed, 

 together with the outer layer of the cortex, and was corky like 

 the latter. The slightly irrregular cells of the cortex were 

 somewhat tangentially elongated; the outermost living cells had 

 rather thick walls. The bundles were often grouped irregularly 

 around the pith; they anastomosed, and in the thicker rhizomes 

 they were not placed in any one circle. The Danish specimens 

 had a few-layered fibrous tissue outside the leptome and a 

 sheath of strong wood-parenchyma on the inner side of the 

 woody part. The Færoese specimen which has been investigated 

 also had this inner arch of stereom, but in the Iceland speci- 

 mens all lignitied stereom was wanting. The endodermis was 

 fairly distinct, and was lignified ; it had tangentially elongated 

 cells. The ceils of the pith were irregular; in an old, Danish 

 specimen there were many scattered sclerenchyma-cells in the 

 pith. The cortex and the pith contained starch. Rhizomes 

 from Greenland have not been investigated. 



