220 botanical gazette. [ September, 



In C 1 , C 2 , Plate xviii, a represents the fir which was later 

 stripped of its branches ; b the one that was used for a con- 

 trol experiment. The slight difference between a and b in 

 C 1 may be attributable to the more exposed position of «, 

 and also to the less compact condition of the lower branches. 

 C 2 shows the temperatures of the two trunks after the 

 branches had been removed from «. It will be seen that the 

 greatest variation before stripping was only about i° C. (see 

 C 1 ), while there was often a variation of 4-5 between them 

 after the branches had been removed from a. It is also no- 

 ticeable that the temperature of the stripped tree begins to 

 fall more rapidly, and that as a rule it was lower than b in 

 the morning. These results point quite conclusively to the 

 fact that the thick coating of foliage which surrounds the 

 trunk accounts, to a large extent, for the lower temperature 

 of evergreen conifers, and that absorption and radiation go 

 on at a much more rapid rate where trees are not provided 

 with winter foliage. 



To see if any material difference existed between the 

 temperatures of woods of different densities, an experiment 

 was first made between a shag-bark hickory (Carya alba) 

 and a cultivated crab-apple tree. The hickory was some- 

 what the larger of the two trees. The specific gravities of 

 the trees show a difference of .1324, the hickory being 

 0.8372, and the Pyrus 0.7048. 2 The borings were made to 

 a depth of 10 cm., and readings were taken for a period of 

 about ten days, but no very great difference was recorded in 

 the temperatures. It may be noted in this connection that 

 there was no very great "difference in the character of the 

 bark, as the bark of the hickory had not begun to exfoliate 



very much. Anptl 



(Quercus alba). Here the dif- 



ference in density is much more marked, the specific gravity 

 of the poplar being .4632, while that of the oak is .747, a differ- 

 ence of over 50 per cent. 2 The borings in this case were not 

 made so deep, in order to see how great a difference existed in 

 the outer layers of the wood proper. The course of these tem- 

 peratures, as drawn in diagram D, plate xviii, shows that the 

 soft wood was far more variable than the denser wood. Not 

 only was the temperature of the poplars considerably higher 

 during the warm part of the day, but it sank from 1-2 below 



Q 



The range in varia- 



tion of the poplar averaging about 16. 5 C. per day, while 



"•Report Tenth Census. Sargent : Forest Tr. s of N. A. 



