448 



THE AMERICAN NATURALIST [Yoh. XL 



membrane and the cell wall to the other end of the cell, thus pro- 

 ducing a flow back through the cell without evident pressure? 

 This seems impossible to answer at the present state of our knowl- 

 edge, but it must be remembered that all theories of pressure pro- 

 duced by unequal permeability must meet this same objection. I 

 believe, however, that a more critical study of the cell will event- 

 ually settle this point. 



Regarding the water in the inner and outer layers, the Vermont 

 Bulleiin gives determinations up to a depth of 15 cm. only, and 

 these are the only ones available. It was found on December 

 13th that the water content of the outer wood was considerably 

 greater than the inner (37.5 ^ and 24 f). From that time until 

 March 11th the percent in the outer layers decreased to 33.4^0 

 while that of the inner wood increased to 39.1 f>, thus giving a 

 greater percentage for the inner layers. From then until April 

 28th there was an increase in both layers, but principally in the 

 inner. At about this time the buds began to open and the water 

 content of both fell abruptly. Along toward the first of June 

 the content of the outer layers again became greater than the inner 

 for a few weeks. These results seemed at first to present an 

 objection to the present theory in that one would expect a greater 

 water content in the outer layers into which the water would be 

 forced from the deeper wood by the pumping action of the pith 

 rays. After further thought, however, I am inclined to believe 

 that the above readings are to be expected. The outer layers are 

 subjected alternately to much greater pressures and suctions, 

 while farther within the fluctuations are moderate, with pre- 

 dominating suction. It is reasonable to suppose that such violent 

 fluctuations would gradually cause the accumulation of gas in 

 these outer layers, and especially since these are near the exterior. 



Why this {)articular temperature of from 1° to 3° C. should be so 

 cfiicifur ill caiHinji: abrupt stinuilation rather than any other is 

 iiUi. ail iiiiMiKfd (|Mestion. It must be noted, however, that 



water from the surface of S|)ir<)<:yr:i 

 and the gradual death of Coleiis ai 

 to this temperature but 



