TREES OF NORTH AMERICA 



(Exclusive of Mexico) 



Class 1. GYMNOSPERM^, 



Ovules and seeds borne on the face of a scale, not inclosed in an 

 ovary ; resinous trees, with stems increasing in diameter by the annual 

 addition of a layer of wood inside the bark. 



I. CONIFER-ai. 



Trees, with narrow or scale-like generally persistent clustered or alternate 

 leaves and usually scaly buds. Flowers appearing in early spring, mostly sur- 

 rounded at the base by an involucre of the more or less enlarged scales of the 

 buds, unisexual, monoecious (dlmcious in Juniioerus)^ the staminate consisting 

 of numerous 2-celled anthers, the pistillate of scales bearing on their inner 

 face 2 or several ovules, and becoming at maturity a woody cone or rarely a 

 berry. Seeds with or without wings ; seed-coat of 2 layers ; embryo axile in 

 copious albumen ; cotyledons 2 or several. Of the thirty-one genera scattered 

 over the surface of the globe, but most abundant in northern temperate regions, 

 thirteen occur in North America. 



CONSPECTUS OF THE NORTH AMERICAN GENERA. 



Scales of the pistillate flowers in the axils of persistent bracts ; ovules and seeds borne 

 directly on the scales. 



Abietine^. Scales of the pistillate flower numerous, spirally arranged ; ovules 2, 

 inverted ; seeds attached at the base in shallow depressions on the inner side of the 

 scales, falling from them at maturity and usually carrying away a scarious wing ; 

 leaves fascicled or scattered [deciduous in Larix). 

 Fruit maturing in two or rarely in three seasons. 

 Leaves fascicled, needle-shaped. 



Leaves in axillary 1-5-leaved clusters, inclosed at the base in a membranaceous 

 sheath ; cone-scales thick and woody, much longer than their bracts. 



1. Pinus. 

 Fruit maturing in one season. 



Leaves in many-leaved clusters on short spur-like branchlets, deciduous ; cone- 

 scales thin, usually shorter than their bracts. 2. Laris. 

 Leaves scattered, linear. * 

 Cones pendulous, the scales persistent on the axis. 



Branchlets roughened by the persistent leaf -bases ; leaves deciduous in dry- 

 ing ; bracts shorter than the cone-scales. 



Leaves sessile, 4-sided, or flattened and stomatiferous above. 3. Picea. 

 Leaves stalked, flattened and stomatiferous below, or angular. 4. Tsuga. 



