361 



thickened and often also lignified parenchyma inchiding the 

 endodermis formed the stereom on the inner side of the strand; 

 the endodermis on the outer side of the fibrous tissue outside 

 the leptome is much thicliened and lignified. Between the 

 rudimentary cambium and the vessels which lie scattered in 

 the wood-parenchyma there occurs a mass of wood-paren- 



Fig. 15. R. acer. 



A, Transverse section of leaf (Greenland; iW/'i). B, 1, Longitudinal section through leaf- 

 apex with epithema (cross-hatched), o. Upper surface ; m, lowers urface (-''/j). 2, Tracheids 

 with epithema-cells (Greenland; ^^li). C, Club-shaped hair from the upper surface of the 

 leaf. D, Small ordinary form of hair from leaf (Denmark; '^/i). E, Octahedral crystal 

 lying in a hair from leaf (Denmark; ^"/i). 



chyma; and between the vessels and the endodermis, a larger 

 or smaller portion of non-lignifled parenchyma is found. Ligni- 

 fied stereom is quite absent from the young peduncle and not 

 until after flowering does it develop. The pith is almost 

 entirely broken down quite early. The hairs are unicellular, 

 fairly thick-walled and slightly lignified. 



The Greenland and Iceland specimens, with the exception of 

 the above mentioned modifications, resemble those from Denmark. 



