74 



in obedience to transpiration, not being compensated by absorp- 

 tion from below ; and also to the fact that when we put the 

 plant in water the cell-walls of the injured cells swell up and 

 become mucilaginous, and they soon cover over the cut surface 

 mechanically with a pellicle of abundant gummy matter ; this 

 rapidly becomes filled with Bacteria, and in this way shuts off 

 the interior of the cut stem from any contact with the sur- 

 rounding water. Every circumstance which tends to increase 

 this loss of water tends also to increase the loss of conducting 

 power, and causes the shoot which is placed in water to wither 

 more rapidly and more completely. We must, therefore, 

 assume that the conducting power of the cells depends on the 

 quantity of water which their cell-walls contain. That this 

 assumption is a very probable one, we can show by forcing 

 in water from below, under pressure, in the manner before de- 

 tailed ; — i. e., if we artificially increase the amount of water in 

 the cells of this piece, we can also increase its conducting 

 power. If the withered shoot or flower be placed in water 

 of from 3 5 to 4o°C. it will soon revive, and if then placed in 

 water of 20°C. it will either remain fresh for days, as e.g., in the 

 Elder, or at least wither more slowly, as e. g. in the Artichoke. 



If we are placing in water for purposes of experiment, the 

 ends of shoots which have begun to wither after being cut off, 

 it is only necessary to remove a second portion from the stem 

 by means of a new cut made a sufficiently long distance above 

 the original point of section, but this time under water, and the 

 shoot revives. This applies also to cut flowers, which, under 

 these conditions, remain much longer fresh than they would 

 otherwise do. As regards the length of the portion necessary 

 to be removed, it has been found that in the Elder (Sanibucus 

 nigra) to remove a portion six centimetres long in a herbaceous 

 shoot of twenty centimetres was amply sufficient. In this last 

 case of section under water, the water is immediately conveyed 

 upwards, and the cells above the point of section recover their 

 turgidity, so that then there is no loss of conducting power. 



We have still to consider certain other phenomena. 



It is well-known that if we prune a Vine in spring, before 



