APPENDIX II. 547 



Slender, compact trees of Acerplatanoides, Fagus, Pinus Laricio, or 

 Abies excelsa, are sawn through at the base, somewhat obliquely, and 

 under a strong current of water, which must be directed towards the 

 cut surface. The trees, say 20 m. in height, are first left standing 

 for half an hour in water ; they are then raised by means of pulleys, 

 and the cut surface after being smoothed is placed in contact with 5-10 p.c. 

 Copper Sulphate solution. 



The trees with which Strasburger experimented, in the course of several 

 weeks or months, and under favourable conditions for transpiration, took 

 up large quantities of the Copper solution. It rose, as could easily be 

 proved, to the tops of the trees, so that the leaves gradually died, and the 

 wood of the stems became more or less completely saturated with Copper 

 salt. Here then the ascent of the water cannot have been caused by the 

 osmotic activity of living cells of the wood, since the Copper salt would 

 of course kill these cells when it came in contact with them. 



Bearing in mind these experiments with large plants, interest attaches 

 also to the results of experiments with small objects in which a portion 

 of the channel of conduction has been killed. If, by immersion in boiling 

 water for half an hour or an hour, we kill the lower part of branches of 

 Populus or Salix to a length of say 20 cm., their upper leafy parts remain- 

 ing uninjured, and then place the branches in eosin solution, they still 

 suck up in course of time large quantities of fluid. Similarly if shoots 

 are placed, immediately after being cut, with their base in 5 p.c. Copper 

 Sulphate solution, the fluid rises to a considerable height in them, although 

 the salt kills the living elements of the wood. 



To understand the movement of water in the plant, it is important to 

 remember that the channels of conduction in the wood, as they are de- 

 veloped, i.e., from the time of germination onwards, fill with water. 

 Hence the peripheral regions of the wood, in their tracheal elements, con- 

 tain for the most part, even at times of vigorous transpiration, only 

 water and no air, while of course the central elements of the wood may 

 be devoid of water. Radial sections of stems or branches of Abietinese 

 are very suitable for examination. 5 The sections should be 1-2 cm. in 

 length and of such a thickness that at least one layer "of tracheides re- 

 mains unopened. Investigation of the sections teaches that in general the 

 aqueous contents of the elements falls off in quantity from without in- 

 wards. 6 



When no transpiration is taking place, the water is retained in the 

 channels of conduction by the adhesion which the wood substance exerts 

 on it, and by the cohesion of the particles of the water, which and 

 Askenasy lays very special stress on this is exceedingly great, and no 

 severance of the water threads takes place. 



When now the sun's heat brings about transpiration, and the leaf cells 

 lose water, they endeavour to replace the loss. They withdraw fluid from 

 the channels of conduction in the vascular bundles ; they exert a tension 

 on the water in the tracheal channels, which, owing to the great cohesion 

 of the water particles, is transmitted right into the roots, and there gives 

 rise to renewed absorption of water. These views of Askenasy as to the 

 nature of the movement of water in the wood certainly merit attention ; 

 the chief stress is always to be laid on the magnitude of the cohesive 

 forces which the molecules of water exert on each other. 



