s 



BULLETIX 1263, U. S. DEPARTMENT OF AGRICULTURE 



Table 1. — First test of heat resistance in moist, hot air, 30 days after solving, 



July 30, 1922. 



[Five seedlings of each species used in each test.] 



Subtest No. 



Oven 

 temper- 

 ature. 



Expo- 

 sure 



time. 



Number of seedlings wilting 

 species and by 



afrer exposure, classified by 

 elapsed time. 1 



Western 

 yellow pine. 



Lodgepole 

 pine. 



Douglas 



n, 



Engelmann 

 spruce. 



4 2 



°F. 

 111.0 

 122.0 

 124. 

 125.5 

 128.0 

 132.5 

 134.5 

 135.0 

 137.0 

 138.0 

 139.0 

 143.3 

 148.0 

 149.7 

 150.5 



Min. 

 6 



10 

 2 

 5 

 5 

 4 

 3 

 2 

 3 

 5 

 2 



2.5 

 1 

 3 

 4 



2-0-0-1-0-0-0 

 3-O-0-0-0-0-1 

 0-0-0-O-1-2-0 

 0-2-1-0-0-0-0 

 3-0-0-0-0-0-1 

 3-0-0-0-0-0-0 

 1-0-0-1-1-0-0 

 0-0-0-1-1-0-3 

 3-0-2-0-0-0-0 

 5-0-0-0-0-0-0 

 0-0-0-2-1-0-0 

 4-O-0-1-0-O-0 

 0-0-0-0-5-0-0 

 5-0-0-0-0-0-0 

 5-0-0-0-0-0-0 



1-0-1-1-0-1-1 

 2-0-1-0-0-0-0 

 0-1-0-0-3-0-1 

 3-0-1-0-0-0-0 

 3-1-0-0-0-0-0 

 1-0-1-0-1-0-0 

 2-0-0-2-0-1-0 

 0-0-0-0-2-1-2 

 2-0-3-0-0-0-0 

 3-0-0-0-2-0-0 

 0-0-0-2-0-1-0 

 3-0-0-1-1-0-0 

 0-0-0-0-3-0-2 

 4-0-1-0-0-0-0 

 5-0-0-0-0-0-0 



0-0-0-1-0-2-0 

 4-0-0-0-0-0-0 

 0-0-0-0-1-0-1 

 O-O-l-l-O-O-O 

 3-0-0-0-0-0-0 

 1-0-0-0-1-1-0 

 0-0-0-2-0-1-0 

 0-0-1-0-1-0-3 

 4-0-1-0-0-0-0 

 2-0-0-0-3-0-0 

 0-0-0-2-0-0-0 

 1-0-0-1-2-0-1 

 0-0-0-0-4-0-1 

 2-0-2-0-1-0-0 

 5-0-0-0-0-0-0 



0-0-2-1-O-O-0 



5 



2-0-O-1-0-O-0 



6 



0-0-O-0-0-2-1 



1. 



1-1-0-1-0-0-0 



3 



2-2-0-0-0-0-0 



9 



1-0-0-0-1-1-0 



S 



0-1-0-1-0-1-0 



11-. 



12 



0-0-0-1-0-2-2 



2-0-0-0-0-1-2 



10 



1-0-0-1-3-0-0 



7 



0-0-0-1-0-1-1 



15 



1-0-0-1-0-0-3 



16 



0-0-0-0-1-0-4 



14. 



2-0-1-0-0-0-2 



13 



5-0-0-0-0-0-0 







Total 











34-2-3-6-9-2-5 



29-2-8-6-12-4-6 



22-0-5-7-13-4-6 



17-4-3-8-5-8-15 



Grand total . 



61 



67 



57 



60 











Per cent . 



76.2 



S3. 8 



71.2 



75.0 







1 The seven divisions under each species correspond to minutes of elapsed time after removal from oven, 

 in the following order: 0-4-10-20-60-180- over 180. 



2 Subtest No. 2 was made at 101°, with a 2-minute exposure, no seedlings wilting. 



TTie reactions of all species were much alike; in fact, no species 

 can be said to be decidedly more resistant than any of the others 

 under conditions which tend to eliminate all transpiration, and 

 therefore to put the species on a basis of equality. Lodgepole pine 

 suffered most, losing 100 per cent by wilting at a temperature of 

 124° F. for 2 minutes; 40 per cent, however, survived 139° F. in a 

 different subtest for the same period. In a third instance all species 

 withstood 139° F. for 2 minutes, while in another group all lost 100 

 per cent when submitted to 135° F. for 2 minutes. The explanation 

 of these variations is not readily discernible. It does not seem prob- 

 able that the seedlings of all species should have been stronger in one 

 instance than in another. The variations are more likely to have 

 been due to differences in humidity, which near the critical tempera- 

 ture is probably the decisive factor. All trees were destroyed at 

 148° F. with a 1-minute exposure, and from study of Table 1 it seems 

 that approximately 141° F. for a period of 1 minute may be con- 

 sidered critical for all species. A total of 80 seedlings of each species 

 was used. The totals lost in all tests, which may be indicative of 

 relative resistance, were as follows: Douglas fir, 57; Engelmann 

 spruce, 60; western yellow- pine, 61; and lodgepole pine, 67. 



The pines exhibited the disastrous effect of too much heat by wilt- 

 ing more promptly than spruce or fir, but suffered no more severely 

 a Her longer periods. The pines are more succulent at this early ago, 

 and their morphological structure is not so strong in relation to 

 their size as that of spruce and fir. Sixty-nine per cent of the 

 yellow pine, G(j per cent of the lodgepole, 56 per cent of the fir, and 



