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water by transpiration, withering will not begin till a later 

 period, and will increase but slowly after the cut surface is 

 placed in water, and the leaves again can transpire. 



The cause of withering in all these experiments is an inter- 

 ruption in the power of conducting water from below, and this 

 is due not only to the conduction of water ceasing for a short 

 time, but also — and this is the more important element of the 

 two — by a change taking place, which consists in the loss of 

 water above the cut surface when the section is made in air, 

 for section in air disturbs the relation existing between the wa- 

 ter and the solid micellae in the walls of the wood-cells, and 

 hence exerts a distinctly injurious influence on the conducting 

 power for water of the wood-cells in the stem, and diminishes it, 

 because under the altered conditions water can no longer pass 

 in the cell-walls with the same ease that it previously did. 

 The loss of water cannot be restored simply by placing the 

 cut surface once more in contact with water : for, when so 

 placed, it takes it up but very slowly. That it diminishes the 

 conducting power for water, we can easily show. If we cut off 

 the stem of a Sunflower {Helianthus annuus) in the air and 

 place it in water and allow it to remain for some time so that 

 it begins to wither, and if we then carefully remove several of 

 the lowest and largest leaves from the stem, we shall find that 

 the growing apex and the leaves which are left will, after some 

 time, begin to revive, even without any further cutting of the 

 stem, which, as we shall presently see, restores conductivity. So 

 that we see that the amount of water which is required to 

 supply the transpiration of a large number of leaves cannot be 

 conducted through the stem after it has been cut off in air, 

 while the amount which is required to supply the transpiration 

 of a few leaves, can ; or, in other words, the cause of this is a 

 diminution of conducting power for water, if the cut surface 

 does not remain too long in contact with air, because a short 

 exposure to the air increases the diminution to a much greater 

 degree. This change occurs only in a short piece of the stem 

 above the cut surface, and it is evidently due to the loss of 

 water from the cells, caused by the suction of the higher parts 



