112 
with large intercellular spaces between the trabeculæ. 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 the 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 trabecule 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.) 
BôürGesex, 1895, pp. 234—235. Secerstenr, 1894, p. 34. 
O. G. Petersen, 1901, p. 74. Hesserman, 1900, p. 27. 
The specimens I have had for investigation are from the 
following localities: — West Greenland: Itivnek (July 1884, 
E.W.). Iceiand: Thingvellir (June 8, 1884) ; Mossfellsheidi (June 14, 
1895); loc. ign. (Jan. 6, 1894, H. Jonsson). Norway: Bosekop 
(July 7, 1885, E. W.); Sakkabani, 1000’ (1885, E. W.); Tronfjæld. 
(Denmark: wood at Hjortlund (July 21, 1892); Mölhede; Botanic 
Garden in Kjebenhavn. 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 
