154 SEEDING AND PLANTING 



subject green or wet cones to a temperature above 122 F. for a period 

 sufficiently long to permit seed extraction. 



Properly cured cones of white pine readily open at a tempera- 

 ture of from 110 to 115 F. after 6 or 8 hours in the kiln. On 

 the other hand, the cones of jack pine are particularly resistant 

 to opening, requiring a temperature above 130 F. for at least 12 

 hours. The temperature should be raised as quickly as possible 

 to that most suitable for the species after the cones have been 

 placed in the kiln. As soon as they begin to steam the ventilators 

 should be opened to carry off the moisture-laden air. The length 

 of time required for the cones to open varies greatly with the 

 species, the ventilation, and the temperature. There is also a 

 great variation between different cones of the same species, some 

 requiring two or three times as long as others. From 1 to 10 

 hours will usually suffice for the drying of all except the most 

 resistant species. When the heating is prolonged it is often ad- 

 visable to withdraw the cones from the kiln before all are opened, 

 later returning the unopened ones for further drying. 



18. The Necessity for Adequate Ventilation. As moist heat 

 is much more destructive to seed vitality than dry heat, adequate 

 facilities for ventilation must be provided. When the drying is 

 done in an improvised room heated with a stove, openings which 

 can be opened and closed at will should be made near the floor and 

 in or near the ceiling. By the control of the incoming and outgoing 

 air, the moisture arising from the drying cones is carried away. 

 Small kilns into which hot air is conducted in pipes permit of 

 much better regulation of both temperature and moisture. The 

 air enters the kiln already heated and the humidity is regulated 

 by the rapidity with which it passes through the kiln and out of 

 the ventilators. 



In large kilns the hot air is forced through the enclosed chamber 

 and kept in continual circulation by blowers. In improvised 

 rooms and small kilns a thermometer is located in a position that 

 will best show the average temperature of the entire heated space. 

 In large kilns a self-recording thermometer and a hygrometer are 

 placed so that they may be observed through a glass door com- 

 municating with the outside. The ventilators should be opened 

 sufficiently to lower the relative humidity below 50 per cent during 

 the early period of the drying and below 10 per cent before the 

 cones are removed from the kiln. 



