12 Henry H. Dixon. 



stem. Jan se, at first, assumed that this wilting is due to the inter- 

 ference with the vital sap-raising functions of the wood parenchyma 

 and the consequent failure in the water supply. He also conceived 

 that the pumping- action of the medullary-rays is polarized, water 

 being regularly absorbed on one side and expelled on the other. 



Westermaier ^), who stated his views about the same time 

 as Godlewski, also maintained the water-raising function of the 

 cells in the wood. But, while Godlewski believed the major part 

 of the motion to take place in the tracheal tubes. West er mai er 

 considered the upward passage to be effected in the wood parenchyma, 

 while the vessels and tracheids acted as water reservoirs rather than as 

 conducting pipes. Godlewski contrasts his view and W es fer- 

 mai er s 's by stating that he holds the wood parenchyma cells to 

 correspond to the piston and the tracheae to the tube of a pump, 

 while the latter holds that the cells act as tube and piston and the 

 tracheae are the reservoirs. Furthermore West er m ai er assumes 

 that the water is held by capillarity in the tracheae in the form of 

 short columns of water alternating with columns of air. 



It is evident that Godlewski and Westermaier saw the 

 difficulty of assuming that the water once set free from the cells 

 would move upwards rather than downwards. Godlewski supposed 

 that the difference in air pressure above and below decided its 

 movement. Westermaier believed it is held by capillary forces 

 in the tracheae at the level to which it is raised by the cells. 



According to the first assumption, however, we are reduced to the 

 theory that the whole upward motion is due to a difference of air 

 pressure above and below. Inasmuch as this difference is never so 

 great as one atmosphere, a rise of more than 103 m cannot be 

 accounted for. 



Neither could Westermaier's hypothesis be followed, inas- 

 much as it was known that the major part of the motion of water 

 upwards takes place in the tracheae and not in the living cells 

 which, as a matter of fact, offer a great resistance to the passage of 

 water. It was also rendered invalid owing to tlie fact that water 

 is free to stream past the bubbles and that they do not offer support 

 for the water in the wood but only increased resistance to its down- 

 ward motion. This was made evident by the 'drop experiment' ascribed 

 to Sachs and H a r t i g , and also by S c h w e n d e n e r 's "^j observation, 

 that the bleeding sap does not carry the bubbles with it from the 



^) M. Westermaier, Zur Keuutniss der osmotischen Leistungen des lebenden 

 Parenchyms. Ber. d. Deutsch. Bot. Gesell., 1, 1883. Die Bedeutung todter Röhren 

 und lebender Zellen für Wasserbewegung. Sitzb. Preuss. Akad. d. Wiss., 48. 1884. 



^) S. Schwendener, Zur Kritik der neuesten Untersuchungen über das Saft- 

 steigen. Sitzber. d. Preuss. Akad. d. Wiss., 44. 1892. 



