360 



What has been said above with regard to the rhizome 

 appUes also to the structure of the stems, viz. that the speci- 

 mens from Iceland which have been investigated have a smaller 

 amount of lignifled stereom than those from Denmark. The 

 Greenland specimens were similar on the whole to those from 

 Iceland. The epidermis also was stronger in the Danish speci- 

 mens (outer walls about 6/j thick) than in the others. The 

 cuticle was striped; the stomata were situated on a level with 

 the surface. The Greenland and Iceland specimens had much 





end 



Fig. 14. R. acer. 



A, Portion of transverse section of stem (Greenland; about ^l\). _p,_iVon-lignifled 



parenchyma; between leptome and xylem there is some луооа-рагепсЬуша; the letters 



as in Fig. 10, B. Б. Base of hair with the epidermis and the outermost layer of 



cortex of peduncle (Greenland; ^'c/i). 



chlorophyll in the epidermis, the Danish had none at all or 

 but little. 



Of the 6 — 10 layers of the cortex the outer are richer in 

 large intercellular spaces than are the inner; but none are 

 present between the epidermis and the subepidermallayer. 

 The bundles (Fig. 14,^) range in number from ten to mauy^and 

 are unequal in size. In the Danish specimens the fibrous tissue 

 outside the leptome attains a thickness of as many asinine 

 layers and is very strong; the thickness of the interfascicular 

 lignified parenchyma is as great as six layers and it has, in 

 some parts, somewhat thickened walls. A few layers of somewhat 



