AIR TN THE WOOD-CELLS, ETC. 269 



air from without can only penetrate into the cavities of young vessels and wood- 

 cells with difficulty, when the latter lose the protoplasm and sap with which they 

 were previously filled. Meanwhile, without entering more into detail respecting this 

 point, it is obvious that the air in the wood-cells, which is always rarefied, must become 

 still further expanded and rarefied if a great portion of the water contained in them 

 is quickly conveyed through the wood cell-walls to the transpiring leaves. Höhnel's 

 experiment, moreover, as I have shown, may be made more evident so far as 

 the vessels are concerned, with dark solutions of colouring matter; and again, 

 I have, by cutting off the branches of living Conifers under a solution of 

 lithium, also been able to convince myself that this solution quickly penetrates to 

 a considerable distance into the wood-tissue. This is to be recognised by the 

 spectroscope, in the manner previously indicated ; and demonstrates anew that 

 the air in the wood-cells as well as in the vessels is rarefied. 



It is clear that these facts may be employed to explain several still obscure 

 phenomena concerning the water contained in the wood of living trees. The 

 obscure facts to which I here refer consist, not in that the water ascends in the 

 wood cell-walls up into the crown of the highest trees, since this, as w^e saw 

 before, is quite intelligible from the imbibing force of the wood cell-walls : it has 

 been hitherto unintelligible, however, how the liquid water comes into the cavities of 

 the wood-cells. If only woody plants of a few metres high were concerned, or the 

 lower portions of a tall tree stem, one might believe that the rarefaction of the 

 air in the wood-cells acts as a sucking apparatus. But every such suction is simply 

 nothing more than the difference of pressure between the atmosphere and the 

 rarefied internal air. Thus, if the cavity of the wood-cells were entirely empty 

 of air, and devoid of aqueous vapour, the suction, or, what is the same thing in this 

 case, the whole external pressure of the air could only force the water about 

 ten metres high in the wood of the stem, even if the cell-walls opposed no 

 resistance. 



It still remains unexplained, moreover, how the action of the atmospheric 

 pressure on the surfaces of the root is to be imagined. Moreover, the wood- 

 cells situated much higher in a tree contain liquid water, in addition to air, and 

 this at any rate cannot be explained so simply by differences of atmospheric 

 pressure. 



Meanwhile, I only bring these doubts forward here because they render 

 clear the question with which we are concerned. Sooner or later it will yet be 

 shown that the rarefaction of the air in the wood, in combination with peculiar 

 arrangements not understood hitherto, brings it about that liquid water gets into 

 the wood-cells, even at considerable heights. Concerning this, also, I may mention 

 that the rarefaction of the air is easily observed even in the vessels of small 

 herbaceous plants; and that a fact so general can certainly not be accidental 

 and without significance for the life of the plant. Whether it may be regarded 



and vessels with such force that the latter become completely empty. Vapour under a pressure 

 corresponding to the temperature alone remains in their cavities. When observations show that 

 air (though very much rarified) is contained in the cavities of wood, this must have penetrated by 

 slow diffusion from the exterior. 



