270 BOTANICAL GAZETTE [October 



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solved by Malpighi. But the bubbles do not move. As Vesque 

 himself was first to show, the water moves past the bubbles, 

 without as a rule disturbing their position. In the present state 

 of our knowledge, this seems to require that liquid water be 

 always continuous from one index of it to the next along the 

 wall. If the pull from the leaves is operative around the bub- 

 , bles, there is no known reason why that of gravity should not be. 

 But if it were, the total pull of the water in the stem would seem 

 to have to be equal to that of an unbroken column of water of the 

 same height. And no such pull can be detected. 



Every feature, active or structural, of the environment of the 

 water in the wood is a part of the complex whose composite 

 result is the rise of the water. Modifying any of these features 

 must influence the movement of the water. Of two physiologi- 

 cal factors — removal of the water by transpiration, and the 

 pressure of the atmosphere — we know that in the entire absence 

 of either the water does not rise. Any theory which leaves out 

 of consideration any part of the environment of the water might 

 reduce the rise of it to an equation, but would not prove its right 

 to acceptance. The atmospheric pressure theory, taken alone, is [ 



in this negligent position. To be complete, it must reckon with | 



the tensions, surface or other, and with the friction, external and 

 internal, of water moving in the lumen, against the walls, and at 

 times in the walls of the wood. Absolute completeness, such as 

 would explain the rise of water in beech but not in oak wood, is 

 not at present a goal; but any theory ought certainly to include 

 every phenomenon of the rise of water in many or all trees, or 

 show that those omitted are irrelevant. 



Nothing about the rise of water strikes one who has seen it as 

 more characteristic than its movement between the bubbles and 

 the wall. When transpiration is at all active, the water must 

 travel more than half of its course in this way. It must move 

 very much more rapidly here than in places where it fills the 

 entire lumen. Surely no theory can be complete which does not 

 include a mechanical explanation of this passage of the bubbles. 

 Science has become so broad that no man can be proficient 



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