KEY TO THE GENERA 



BASED LARGELY ON LEAF CHARACTERS 



\. Seeds not in an ovary; flowers unisexual; leaves fan-shaped, 



linear, needle-like, or scalelike 



GYMNOSPERMS, (see A, page xxiii). 



1. Seeds borne in a closed ovary which at maturity becomes the 



fruit ANGIOSPERMS, (see 2). 



2. Leaves narrow with parallel veins; flower parts in 3's or 6's; 

 stems without central pith or annual layers of wood ; embryo 



with a single cotyledon 



MONOCOTYLEDONS, (see B, page xxiv). 



2. Leaves generally broad or rarely wanting, with netted veins; 

 flower parts usually in 4's or 5's; stems with pith and annual 



layers of wood ; embryo with two cotyledons 



DICOTYLEDONS, (see C, page xxiv). 



A. GYMNOSPERMS 



1. Leaves fan-shaped with numerous fine veins radiating from the 

 petiole, deciduous; twigs with spur shoots; fruit a drupelike 

 seed GINKGO, p. xii. 



1. Leaves linear, needle-shaped, or scalelike, with 1 vein, usually 



persistent CONIFERS, 2. 



2. Leaves needle-shaped, in fascicles of 1-5, each fascicle enclosed 



at base by a sheath PINUS, p. 2. 



2. Leaves single, linear or scalelike 3 



3. Leaves mostly linear; leaves and fruit scales spirally arranged. .4 



3, Leaves mostly scalelike; leaves and fruit scales opposite 12 



4. Fruit a woody or papery cone composed of seed-bearing 



scales 5 



4. Fruit a single seed partially or wholly surrounded by a fleshy 

 aril 11 



5. Cone scales thin, terminally attached; seed terminally winged, 



2 to each scale 6 



5. Cone scales peltate; seed laterally winged, 2 to many per scale. 10 



6. Leaves deciduous; twigs with spur shoots LARIX, p. 42. 



6. Leaves persistent; twigs without spur shoots 7 



7. Base of leaves persistent on twigs as peglike projections (sterig- 



mata) 8 



7. Leaves not leaving peglike bases on twig upon falling 9 



8. Leaves sessile, 4-angled or flattened PICEA, p. 48. 



8. Leaves stalked, flat or rounded in cross section . TSUGA, p. 64. 

 9. Leaves sessile; cones erect, the scales deciduous from the axis 



at maturity; buds rounded, resinous (except in A. bracteata) . . . . 



ABIES, p. 72. 



xxiii 



