192 CROWBERRY, HEATHS, ETC. 



Empetrum nigrum, L. Crowberry. Leaves evergreen, 

 numerous, small, sub-sessile, in whorls of 3 or 4 ; or, at the 

 tips of the shoots, spirally imbricate and crowded ; linear, 

 linear-oblong, or acicular, blunt, semi-terete, 4 5 x 1 mm.; 

 margin revolute, glabrous or slightly ciliate ; leathery, 

 shining green above; paler, with a whitish midrib be- 

 neath. Red-brown in autumn. 



Shoots and leaves downy; the latter hardly 

 acute, and in whorls of 4, rarely of 3. 



Erica tetralix, L. Cross-leaved Heath. Leaves in 

 whorls of 4, rarely of 3, acicular or linear-lanceolate, hardly 

 acute, 4 5 x 0'5 1 mm.; margins revolute, ciliate with 

 stiff glandular hairs, pubescent, dark green above, bluish- 

 glaucous beneath, the concave area tapering, and the mid- 

 rib downy. Red-brown in autumn. 



[The rare species Erica ciliaris, with broader, almost 

 ovate, gland-ciliate leaves, E. vagans, with linear pointed 

 leaves, and E. earned with linear blunt leaves may also 

 be mentioned.] 



** Leaves opposite and decussate, not nor- 

 mally in whorls of three ; fleshy and 

 scale-like, short and blunt, or at least 

 not rigid and pungent. 



t Shoots with crowded leaves and flattened. 



Thuja gigantea, Nutt. Arbor Vitse. Tall tree, with 

 flattened shoots of crowded, decussate, sessile and fused, 

 ovate or deltoid, acuminate, scale-like, but bright green 

 leaves, glandular on the back ; or smaller, apiculate and 

 almost devoid of glands. Venation obsolete. Leaves 

 reddish in winter. 



ft Shoots of crowded leaves quadrangular, not 

 flattened. 



