THE BIOLOGY OF LODGEPOLE PINE 415 



to that given off by the cones. Rut opening of cones after this free- 

 water content has been lost in air-drying, involves the use of two to 

 four times the theoretical heat units required to evaporate water. 

 Furthermore, cones from a limestone soil require 15 per cent more 

 heat than those from a siliceous soil. It, therefore, seems to be plainlv 

 indicated, as Clements has suggested, that opening of cones requires 

 more than a mere drying of them ; it requires a certain change in 

 moisture content in a given time. We can now go much farther and 

 say that this change will only be effected, with cones already partly 

 dried, by a tremendous expenditure of heat energy. It is believed that 

 this energy is necessary to overcome the avidity of the cell contents 

 for moisture. The requirements of the limestone cones seem to point 

 to the presence of salts, such as calcium chloride, which have a 

 strong avidity. Be that as it may, it appears that in nature we have 

 at least three distinct causes for the retention of cones, namely, unfavor- 

 able growing conditions, such as a limestone soil,^° causing subnormal 

 development of cones ; factors such as the late development of the 

 individual cones which may cause an unusual flow of both pitch and 

 sap to them; and finally, the insolation of the cone, which may be 

 such as to open it immediately, or may dry it slowly, and cause it to 

 become fixed. Such cones are given a good opportunity to open only 

 after years, when the pedicel breaks or the foliage falls away from 

 the limb and exposes it to direct insolation. The greater number of 

 persistent cones in dense stands points to the last cause as the most 

 important one. Whatever the cause, the effect on silviculture should 

 be evident. Cone retention, which we can only look upon as an ab- 

 normal physiological phenomenon, is directly helpful to the forester. 

 It insures a crop of seed at any time, and we may confidently expect 

 that silvicultural cutting of almost any character will release vast 

 numbers of seed, both from the trees cut and from those left standing, 

 the latter resulting from the accession of more light and heat to act 

 upon unopened cones, and from better growing conditions for the 

 production of later seed crops. In fact, I may say, as a closing word, 

 that to my mind, throughout the area in which lodgepole is already 

 established, silviculture will never confront a failure of reproduction 

 due to lack of seed. Our problem will be to secure cutting heavy 

 enough to insure the soil and light conditions which this species de- 



1" Tower assumes a limestone soil to present favorable growing conditions, whereas 

 t his is true only for a few species specially adapted to it. 



