42 BULLETIN" 327, U. S. DEPARTMENT OF AGRICULTURE. 
of equal age, which favor overhead light to all of the trees. It en- 
dures but little side shade, as is shown by the long, clean trunks it 
produces in close stands and commonly also even in rather open 
stands. Ability to endure shade, however, appears to vary with the 
nature of the soil, available moisture, and climatic conditions, trees 
always showing relatively greater tolerance of shade under the best 
conditions for growth. 
Shasta red fir seeds plentifully, good crops of cones being pro- 
duced about every two or three years. Seed production is usually 
greatest in the more open stands of moderately old trees. The seed 
has a fairly high rate of germination, but under ordinary conditions 
of storage its vitality is retained for only a few months. Germina- 
tion occurs abundantly on moist mineral soil in the open or under 
light shade, being much less frequent or wanting on dry, thick duff. 
Seedlings grow rapidly in cool, moist, sandy soil, soon restocking 
high slopes and openings cleared by fire or storm. 
LONGEVITY. 
Shasta red fir appears to be rather long lived. Trees from 20 to 36 
inches in diameter are from 225 to 3T0 years old. Very large trees, 
not yet studied chiefly because the timber is not now cut for mill- 
ing, would certainly show much greater ages. There are evident 
differences, not yet determined, in the longevity of trees growing on 
high, exposed slopes and those at lower levels in more protected 
places, trees of higher elevations naturally being considerably older 
than those of the same diameter growing at lower levels. 
KEY TO GENERA. 
Leaves four sided; cones hanging down or curved downward, the cone 
scales firmly attached and not falling away when the cones are ripe_ Picea. 
Leaves flat, grooved on the upper side; cones upright, the cone scales 
easily detachable and falling away from a persistent spikelike central 
stem when the cones are ripe Abies. 
KEY TO PICEA. 
Twigs smooth: 
Leaves very keenly pointed and stiff; cones mostly 3 to 4 inches 
long Picea parryana. 
Leaves only moderately sharp-pointed ; cones mostly 1£ to 2\ inches 
long Picea canadensis. 
Twigs minutely hairy : 
Cones firmly attached to the twigs and persistent for a number of 
years Picea mariana. 
Cones lightly attached to the twigs and soon falling from the 
trees Picea engelmanni. 
