EEFOEESTATION ON THE NATIONAL FORESTS. 
11 
which the drying is done. In a well-equipped plant drying may be 
finished in less than half the time required in a tent, even with the 
same temperature. It is therefore impossible to cite average figures 
of general application. Ordinarily, the higher the temperature 
the quicker the drying can be accomplished. Dry heat, however, 
is more effective than moist heat, and heat that is too intense is very 
apt to impair the fertility of the seed. This is particularly true of 
intense moist heat. Often this injury to seed is not appreciated at 
the time, since the deterioration does not become apparent until 
several months later. 
The maximum temperature which should ordinarily be applied 
to all species except lodgepole pine is 120° F. This can be raised 
safely to 130° F. if the air is dry and good ventilation provided. 
Lodgepole-pine cones should not as a rule be subjected to a tem- 
perature of more than 140° F., although this can be raised safely 
to 150° F. under favorable conditions. Lodgepole-pine cones are 
hardest to open; then come, in order, western white pine, western 
yellow pine, Engelmann spruce, and Douglas fir. Douglas fir cones 
can often be dried satisfactorily at a temperature of 110° F. 
Assuming that the cones are mature and moderately dry when put 
into the kiln and that the room is evenly heated and well ventilated, 
lodgepole-pine cones should be thoroughly dried in from 8 to 10 
hours at a constant temperature of 140° F. and other species in from 
10 to 15 hours at a constant temperature of 120° F. Under less 
favorable conditions these periods may be greatly increased. In 
one instance lodgepole-pine cones dried in a tent at 140° F. took 44 
hours to open. The difference Avas due mainly to uneven distribution 
and loss of heat in the tent. Preliminary drying of the cones for a 
few hours at from 80° to 100° F. has been found an advantage. 
Opening will also be hastened by spreading the cones thinly in the 
trays and stirring them frequently to make the drying more uniform. 
Ventilation. — The proper ventilation of drying rooms, while less 
difficult than the even distribution of heat, is fully as important. 
All undried cones contain some moisture. As this is driven off the 
air becomes more and more saturated. Saturated air not only pre- 
vents rapid drying of the cones, but may injure the seed embryos. 
German experiments indicate that damp, cold air is much more 
harmful to seeds than dry, warm air. Some method of ventilation 
(letting in fresh, dry air and letting out moist air) is, therefore, 
essential. 
The method usually employed is to insert one or two ventilators in 
the roof of the building or tent and also in openings near the floor 
for the entrance of fresh air. The amount of air taken in and let 
out can be regulated by adjustment of the ventilators. Tents are 
