174 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



nigra in view) ; and alba, with oval-oblong, or oval-cylindrical cones, 

 pendulous, on longer Vjranchlets than the others, (the geogj-aphical 

 range extending to the Rocky Mountains, on authority of specimen 

 from Bourgeau). 



In Dr. Robert Bell's chart of the northern limits of trees formins 

 the Canadian forests, the two spruces, alba and iivjra are lined 

 together. 



Prof Macoun, in the Catalogue of Canadian Plants of the Geo- 

 logical Survey of Canada, gives two species, combining rubra with 

 nigra. 



Sir Joseph Hooker, in his taVjulation in the Outlines of Distribution 

 of Arctic Plants (Linna;an Transaction.s, 1864), gives only alba and 

 nigra, and Sereno Watson, in the Botany of California, also dismis.ses 

 our spruces in N.E. America as " two species." 



The following descriptions of the several species are not thrown- 

 into systematic form, being merely intended to call attention to 

 points of difference, and to suggest observation and enquiry, so that 

 the necessary information may be obtained for the formation of 

 accurate and jjermanent diagnostic charactei-s : 



1. PiCEA ALBA. — Link, in Linnsea, xv. p. 519. 



Picea alba, the white spruce of Canada, is i-ecognized at a distance, 

 from the allied species, by the comparative massiveness of the foliage 

 with which its horizontal or pendant boughs are clothed, and by its 

 glaucous or whitish-green tint, — the leaves when newly expanded 

 being pale and silvery, as if covered with the most delicate coating of 

 hoar frost. This appearance, however, Ls caused by the individual 

 leaves not being wholly green, but having longitudinal rows of 

 apparently white or colourless dots or spaces, owing to the non-develop- 

 ment of chloi'ophyll in certain surface cells at regular intervals. The 

 old bark of the stem is grayish, not dark-colored, and the young 

 shoots of the year present a smooth, shining, ivory-white surface, 

 altogether destitute of trichomes or roughness of any kind. The 

 leaves vary in actual size with the vigour of the tree, but are longer 

 in proportion than those of either of the other species ; the leaf-bases 

 from which they arise are arranged uniformly around the horizontal 



