APPENDIX II. 



In 84 the problem of the movement of water in the wood was discussed. 

 We saw that the water moves in the ]umina of the conducting wood 

 elements, and if we now go into the matter a little further, it is par- 

 ticularly because Askenasy l has recently published a short treatise, 

 which, in connection with the important work of Strasburger, certainly 

 appears to be of great significance. 



Sachs 2 has already stated emphatically that the root pressure can by no 

 means serve to cover the loss of water experienced by vigorously tran- 

 spiring plants. It is true that in the intact plant water can be raised by 

 root pressure in larger quantities and to a greater height than in a de- 

 capitated plant, since the atmospheric pressure acts on the cut surface in 

 the latter, while in the former the rise of the water cannot be affected 

 by the atmospheric pressure. But for all that, even in the uninjured 

 plant, root pressure by no means plays a part in the movement of water 

 in the wood of strongly transpiring plants, and Hansen 3 showed that 

 even plants with dead roots, which therefore could exhibit absolutely 

 no root pressure at all, still actively transpire. Pot plants of 

 Nicotiana or Helianthus, which bear 6-10 large leaves, are placed, after 

 the soil in the pots has been soaked with water, in double-walled sheet 

 zinc receivers, resting on tripods. The space between the walls of the 

 receivers is filled with water. We place thermometers in the soil, cover 

 the pots with thick card-board covers, halved and cut out in the middle 

 so as to fit round the stems of the plants, and then heat the water. 

 The roots are exposed for an hour or two to a temperature of 70 C. 

 They are then, as may be established by microscopical examination, 

 quite dead. We now carefully wrap the pots in tinfoil, cover the 

 surface of the soil and the stems of the plants with tinfoil, and can 

 then by repeatedly weighing prove that the aerial parts of the plants, 

 if the temperature of the air is not too low, continue for days to lose 

 considerable quantities of water without withering. The dead roots 

 must absorb water from the soil. 



Capillary forces may be of importance in retaining water in the 

 tracheal channels, but, as Strasburger 4 convincingly proved, they play 

 hardly any part in the actual elevation of the water. Nor can we 

 call to our help the atmospheric pressure when we are considering the 

 elevation of water to great heights (e.g. 200-300 ft.), and so one seems 

 obliged to have recourse to the co-operation of the living cells of the 

 wood. 



I may here, however, direct special attention to certain investigations 

 of Strasburger (I.e. p. 607), which it is true I have unfortunately not 

 yet myself repeated, but the results of which undoubtedly appear 

 to merit consideration, 



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