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IOWA ACADEMY OF SCIENCE You XXIX, 1922 
1 . Pinus Pine 
(The classical latin name) 
Broadly cone-shaped or irregular trees of medium size. Lvs. 
evergreen, 4-10cm. long, needle-like, in groups of 2, 3, or 5, with 
a common sheath at base. 
Pollen with 2 empty floats. Fr. a cone of persistent scales, each 
with 2 seeds at base. 
Note: Trees of this genus furnish all of the white and yellow pine 
lumber of commerce. There are 80 species, all in the northern hemisphere, 
20 in North America. Rosin and turpentine and “hard pine flooring'’ are 
taken from the “long leaf pine” ( Pinus palustris ) of the southern states. 
Young shoots of this species are often shipped north for Christmas 
decorations. Cones of the 5-lfd. or “white” pines ripen in one season ; 
those of the 2- or 3-lfd. or “yellow” pines require two summers. 
1. Lvs. in 5’s, slender 2 
1. Lvs. in groups of 2 or 3 on the same tree 8 . P. ponderosa 
1. Lvs. in groups of 2 strictly 3 
2. Lvs. dark green, branchlets smooth i. P. Strobus 
2. Lvs. bluish white oh inner sides; branchlets finely hairy 2 . P. Cembra 
3. Low and shrubby # 4 . P. montana mughus 
3. Trees * 4 
4. Branches covered with old cones ; lvs. short 3 . P. Banksiana 
4. Cones few, not remaining long on tree after opening 5 
5. Lvs. 4-6cm. long ; bark papery, yellow 5 . P. sylvestris 
5. Lvs. 6- 14cm. long; twigs dull orange color 6 . P. resinosa 
5. Lvs. 6-14cm. long; twigs dull grey 7 . P. nigra austriaca 
1. P. Strobus White pine Weymouth pine 
Lvs. in groups of 5, 6-8cm. long, soft and flexible, very dark 
green and feathery in appearance. Branchlets not hairy. Cones 
often curved, 1-1. 5dm. long, slender; scales thin and pliable, 
without spines. Tree 20-50m. tall. 
Stam. fl. oval, 8-10mm. long, with 6-8 bracts at base; pist. fl. 
long stalked, cylindrical. Seed smooth; cotyledons 8-10. 
Sandstone bluffs, very rare here. 
Eldora. Cult., common ; campus. 
Nfd. to Pa. and Ga., Man., Minn, and cent. Ia. 
Fl. May-June. Fr. Nov. -Dec. 
Note: This tree furnishes the true white pine lumber, unrivalled for 
smooth, firm, soft grain, ease of working, and freedom from swelling and 
warping. It is the best ornamental pine for Iowa. One authority pro- 
nounces it the 'most useful tree in the world. The locality at Eldora is the 
farthest natural outlier of the species toward the southwest. The next 
nearest natural occurrence is in Delaware county,' Iowa, P. plexitis with 5 
short stiff curved needles to a bunch is on trial at Ames and in Grinnell. 
2. P. Clmbra Swiss Stone Pine 
Lvs. in 5’s, 5-8cm. long, rather stiff, erect, dark green on outer 
side, bluish white on inner sides. Branchlets finely hairy. 
Tree 20-40m. tall, narrowly and densely conical. Cones ovate, 
6-8cm. long, with broad scales. Seeds 1cm. long, wingless. 
