360 



NVIial lias been said aliove willi re^'ard to the rhizome 

 applies also to I lie slnictiire of the stems, viz. that the speci- 

 mens from Iceland which have been investijirated liave a smaller 

 amount of li.irnified stereom than those from Denmark. The 

 Greenland specimens were similar on the whole to those from 

 Iceland. The epidermis also was stroni.'er in the Danish speci- 

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

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

 the surface. The Greenland and Iceland specimens had much 



Fig. 14. R. acer. 



A, Portion of transverse section of stem (Greenland; about ^/i). p, Non-lignified 



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



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



cortex of peduncle (Greenland; -'"^ 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 subepidermal layer. 

 The bundles iFig. 14, A) range in number from ten to many and 

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

 outside the leptome attains a thickness of as many as nine 

 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 



