418 THE AMERICAN NATURALIST [Vol. XL 



Juglans cinerea. Little gas in vessels, but fibers filled with gas. 

 Branches bled on radiator. 



Nyssa sylvatica. Wood quite highly saturated; little gas in either 

 vessels or fibers. Bled on radiator. 



Cladrastis lutea. Same as Nyssa. Bled on radiator. 



Salix fragilis. Large quantity of gas in vessels and fibers. Not even 

 damp on radiator. 



Catalpa speciosa. Same as Salix. 



Populus dilatata. Vessels almost full of gas. Not damp on radiator. 



Fraxinus americana. Full of gas; could blow through a piece several 

 centimeters long. Not damp on radiator. 



Vitis vulpina. Full of gas. Could blow through. Not damp on 



Pru7iiis virginiana. Large quantity of gas in vessels. Not damp on 

 radiator. 



Quercus alba. Much gas. Could blow through. Did not become 



Regarding tree temperatures, it was found that in holes 8 em. 

 deep they fluctuated less than air temperatures. According to 

 the Vermont Bulletin slight variations in outside temperature 

 caused little or no variation within the tree, which on many days 

 did not show a range of 2° C. Considerable variation in external 

 temperature, how^ever, was follow ed in due time by corresponding, 

 though less marked, internal fluctuation. Temperatures of -3° C. 

 and -2.5° C. were the low^est recorded during the sugar season. 

 Thermometers placed in 2.5 cm. deep holes on the north and south 

 side of a tree showed during the winter a lower registration on 

 the north side at all times except one day when the south w^ind w as 

 blowing. 



The Gas-expansion Theory 



About twenty-five percent of the volume of a maple tree is 

 occupied by gas during the sugar season (Vermont Bull). The 

 presence of so much gas in the wood, together with its ease of 

 detection and its known expansive qualities, early led the attention 



