36H 



sulterizcd. A somewhat thickened, snbexodermal layer occurs 

 and Wio cortex has lari^er or smaller lacunae. The endodermis is 

 somewhat Ihickened and the central cylinder is diarch to tetrarch. 



Fig. 20. E. sulphurcus. 



A, Portion of section of central cylinder of adventitious root of the first order (Scoresby, 

 Sound; "'■'•/i). B. Transverse section of rhizome (Spitzbergen; ^i). C, Portion of trans- 

 verse section of stem (Spitzbergen; about -""/i); b, bast; c, cortex; end, endodermis; <j 

 the large pentagonal sieve-tube; /, lacuna; m, pith; mh, pith-cavity; p, pericycle: ph, 

 leptome; vp, lignified parenchyma; x, xylem. 



There is a large sieve-lube on the outside of each group; 

 cambium is absent (Fig. 20, A). 



The root ol" the second order consists of epidermis, 

 about five layers of cortical cells and a diarch central cylinder. 



The epidermis as well as large 



parts of the cortex are col- 



"^ lapsed; a thickened subex- 



^e^ odermal layer does not occur. 



The epidermis and the in- 



distinct exodermis are suber- 

 ized. Here also a large sieve- 

 tube occurs on the outside 

 of each group of sieve-tissue. 

 Mycorrhizas have been 

 found in specimens from all 

 the habitats and the hyphæ 

 often occur in large quantities 

 in the lower, slender parts of the roots of the first order and 

 in the roots of the second order. Balls of hyphæ, whenever 

 such occur, are most frequently found in the inner cells of 

 the cortex iFig. 21 1. 



Fig. 21. JS. sulphureus. 



Portion of transverse section of root of 



the second order showing mycorrhizas (Nova 



Zembla; '^"ji); ep, epidermis; e.i', exodermis; 



end, endodermis; li, hyphæ. 



