FOREST TREE SEED AND SEED COLLECTING 153 



cones. After the transfer to the kiln a much shorter time and 

 lower temperature is required for their complete opening than 

 when they are transferred to the kiln directly from the storage shed. 



17. The Maintenance of Uniform Temperature. Until 

 recently it was believed that the cones while moist and closed 

 could be subjected to a comparatively high degree of heat but 

 that the temperature must be lowered as drying proceeded. 

 Kilns were constructed, making it possible for the seed to pass 

 into a cooler compartment or room as soon as it was liberated 

 from the cones. Recently Wiebecke 1 and others have conclu- 

 sively shown that a high temperature during the period when the 

 cones, and consequently the contained seeds, are damp is most harm- 

 ful, while the same temperature after the seed has escaped from the 

 cones and is thoroughly dry is least harmful. Thus, green Scotch 

 pine cones taken from the forest and immediately exposed to a 

 temperature of 131 F. for 20 hours, or long enough to permit 

 seed extraction, retained on the average but a 7 per cent germina- 

 tive capacity; while cones from the same lot after passing through 

 a period of storage, preliminary drying, and exposure in the kiln 

 for a period of from 6 to 8 hours at a temperature of 131 F. 

 retained at the close of the run an average germinative capacity 

 of 87.6 per cent. 



The operator of a modern seed-extracting plant is confronted 

 by the two following conditions which are worthy of careful con- 

 sideration, low temperature and increased cost for extraction 

 and high temperature and reduction in seed quality. As high a 

 temperature should be used as is consistent with the retention of 

 seed quality. 



Exhaustive experiments on the cones of Scotch pine and Nor- 

 way spruce by Haack prove that the temperature must be gauged 

 with extreme care, as an increase of only a few degrees above a 

 non-injurious temperature may be very harmful. Haack recom- 

 mends a constant temperature of 122 F. as the permissible heat 

 for green cones. If the cones are dry when gathered or have 

 been thoroughly cured, a temperature of 131 F. is permissible. 

 Although some species, as illustrated in jack pine and lodgepole 

 pine, will resist a higher temperature than others, it is not safe to 



1 Wiebecke, Forstmeister: Die Anwendung neuen Erkennens und Konnens 

 auf die Kiefernsamendarre. (Zeitschrift f. Forst- u. Jagdwesen, S. 342-360. 

 1910.) 



