RELATIVE RESISTANCE OF TREE SEEDLINGS TO EXCESSIVE HEAT 9 



50 per cent of the spruce wilted within the first 15 minutes. In prac- 

 tically all instances the injurious effect of high temperatures was 

 shown first by the needle tips, which, because of their small masses, 

 would naturally become heated more quickly. 



It is believed that this test of the 30-day seedlings more nearly 

 furnishes an expression of the effect of injurious temperatures upon 

 the protoplasm itself than do the tests upon the older seedlings, be- 

 cause of the fact that transpiration was of minor consequence. In the 

 saturated atmosphere maintained throughout, the pines could not 

 take advantage of their power of transpiring more readily than the 

 others and thereby keep down internal temperatures. The great 

 difficulty in any tests of this nature lies in the inability to separate 

 the transpiration factor from the heating factor which might more 

 immediately cause the coagulation of the protoplasm. Therefore, by 

 eliminating transpiration it was to be expected that all species would 

 react alike to high temperatures, assuming all protoplasms to be sub- 

 ject to coagulation at the same temperatures. It should be noted, 

 however, that while test 1 comes nearest to eliminating transpiration, 

 it is conversely farthest from simulating actual field conditions. 



RESULTS IN DRY AIR 46, 64, AND 90 TO 92 DAYS AFTER SOWING. 



Since these three tests were performed in a similar manner, and the 

 results obtained were much alike, they will be considered together. 

 The results at the ages of 46, 64, and 90 to 92 days, respectively, are 

 shown in Tables 2, 3, and 4. The subtests are arranged in each table 

 in the order of maximum temperatures recorded. 



Table 2. — Second test of heat resistance. Exposure to radiation from elec- 

 tric coil 46 days after sowing, seedlings transplanted in sand. 



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





Pot No. 



Maxi- 

 mum 

 tempera- 

 ture 

 in air. 



Maxi- 

 mum soil 

 tempera- 

 ture. 



Ex- 

 posure. 



Number of seedlings dead, mortally injured, 

 slightly injured, and uninjured, by species. 1 





Western 

 yellow pine. 



Lodgepole 

 pine. 



Douglas Engelmann 

 fir. I spruce. 



1 . . 



F. 

 90.5 

 106.7 

 116.6 

 137.8 

 154.8 

 165.2 

 172.4 

 176.4 

 176.4 

 181.8 



78.7 

 88.7 

 98.2 

 112.3 

 118.3 

 134.2 

 121.2 

 117.6 

 118.3 

 122.4 



Min. 

 10 

 10 

 14 

 13 

 10 

 10 

 8 

 5 

 6 



0-0-0-6 



0-0-0-6 



0-0-0-6 



0-0-0-6 



1-0-0-5 



i 3-0-2-1 



6 2-1-2-1 



0-0-1-5 



3-0-1-2 



6 2-1-1-2 



0-0-0-6 



2 0-0-0-5 



0-0-0-6 



0-0-0-6 



0-0-0-6 



2-0-1-3 



6 2-0-1-3 



1-0-0-5 



0-0-0-6 



6 1-0-0-5 



0-0-0-6 

 0-0-0-6 

 1-0-1-4 

 3 0-0-0-6 

 3 5-1-0-0 

 6 6-0-0-0 

 6 6-0-0-0 



0-0-0-6 



2 



0-0-0-6 



3 



0-0-0-6 



4 _ 



0-0-0-6 



5 .. 



3 1-1-1-3 



10 



5 6-0-0-0 



9 



6 4-0-2-0 



6 



» 6-0-0-0 



3 6-0-0-0 



7 



3 6-0-0-0 1 3 6-0-0-0 



8 _— _ 



« 6-0-0-0 5 5-0-1-0 











147.9 



111.0 



9.3 



| 





Total 







11-2-7-40 



6-0-2-51 



36-1-1-22 I 28-1-4-27 

















Si _4-i 4-1 40 



















i The four divisions under each species refer, respectively, to the following degrees of injury: Dead 

 seedlings; injured seedlings that will die; injured seedlings that will live; uninjured seedlings. 



2 Only five lodgepoles transplanted into this pot. 



3 All seedlings in pot slightly cooked. 



* Three of the seedlings cooked during exposure. 



5 All seedlings cooked. 



6 One seedling cooked. 



