50 PINACEAE. 
8. Needles blue-green. P. sylvestris. 
Needles yellow when young. P. sylvestris aurea. 
9g. Needles rather short (under 8 cm.). Io. 
Needles rather long (over 9 cm.), dull. 12. 
10. Twigs glaucous. P. viginiana. 
Twigs not glaucous. II. 
ai.. Tree. P. montana. 
Round shrub. P. montana Mughus. 
ra.oTrees, 13, 
Shrub. - P. nigra pygmaea. 
13. Pyramidal. P. nigra. 
Round-topped. P. nigra austriaca. 
14. Bark orange. P. nigra cebennensis. 
Bark rather red: needles glossy. P. resiriosa. 
15. Needles moderately long (under 15 cm.). P. rigida. 
Needles very long (over 15 cm.). P. Taeda. 
16. Twigs glabrate. 17. 
Twigs tomentos:. P. Cembra. 
Ty LCE. 1G; 
Dwarfed. Io. 
18. With spreading branches. P.’ otrobtis, 
With ascending branches. P. Strobus fastigiata. 
19. Needles very glaucous, P. Strobus alba. 
Not very glaucous, 20. 
20. Bush-like. P. Strobus brevifolia. 
Umbrella-shaped. P. Strobus umbraculifera. 
Prostrate. P. Strobus prostrata. 
ScrApopitys. Umbrella Pine. 
Evergreen percurrent trees with ductless soft white wood 
without resin passages; moderate fluted buff twigs swollen at 
intervals; continuous pith; no stipule scars; alternate persistent 
ciliate scales whorled at the swollen nodes and each then with 
a long linear phylloid shoot in its axil; monoecious catkin- or 
cone-like naked flowers; and .cones with several-seeded scales. 
“Leaves” green, grooved, revolute. S. verticillata. 
