112 



with large intercellular spaces between the trabeculae. This 

 central part again merges gradually into a part which usually 

 consists of two layers of cells, and which may be termed the 

 palisade- tissue of the lower surface. Thus, there is a certain 

 isolaterality in the leaf of Lyonia as in that of Arctostaphylos 

 Uva-ursi, which species tht; present one resembles in regard 

 to its mesophyll. Of these two species Lyonia has the more 

 isolaterality which is connected with the fact that the leaves 

 of this species are sometimes vertical. 



Beneath the larger vascular bundles an ill-developed aqueous- 

 tissue occurs, with trabeculae of thick-walled cells of similar 

 nature to those in Ledum and others. The stereom, which is 

 of medium thickness, consists of libriform cells. 



The limits of the annual rings were very indistinct in the 

 material from the Botanic Garden in Kjøbenhavn (0. G. Peter- 

 sen, p. 76). 



Arctostaphylos Uva-ursi (L.) Spreng. (Figs. 26—27.) 



BÖRGESEN, 1895, pp. 234—235. Segerstedt, 1894, p. 34. 

 O.G.Petersen, 1901, p. 74. Hesselman, 1900, p. 27. 



The specimens 1 have had for investigation are from the 

 following localities: — West Greenland: llivnek (July 1884, 

 E.W.). Iceland :Thingvellir (June 8, 1884); Mossfellsheidi (June 14, 

 1895); loc. ign. (Jan. 6, 1894, H. Jonsson). Norway: Bosekop 

 (July 7, 1886, E.W.); Sakkabani, 1000' (1885, E.W.); Tronfjæld. 

 [Denmark: wood at Hjortlund (July 21, 1892); Mölhede; Botanic 

 Garden in Kjøbenhavn. Switzerland: St. Moritz.] 



The leaf. The upper and lower epidermis are very much 

 thickened (on an average as much as 16//) by the presence of 

 a thick cuticle aud beneath it a cuticularized layer. Lateral 

 walls not undulating. Hairs occur only along the margin of 

 the young leaf and are not of much importance. The stomata, 

 which are confined to the lower surface, are somewhat sunk 



