IV.] VARIOUS THEORIES, &c 117 



In Pringshetm's Jahrbucher for 1884 appeared a 

 remarkable and brilliant paper by Emil Godlewski/ 

 which placed the whole subject in an entirely new 

 position, and seems to have practically closed the 

 discussion as to principles; the papers subsequently 

 published dealing with particular points only. 



The paper opens with a critical examination of 

 the previous theories, especially those of Boehm and 

 Hartig, and the author collects what is proved by 

 investigation so far. 



Water and air always exist in the lumina of the 

 tracheides, &c., and the movement takes place in the 

 lumina : the imbibition theory of Sachs may be regarded 

 as overthrown by the subsequent researches of Vesque, 

 Elfving, Russow, Hartig and others. 



As to the mechanism of the process, several points 

 have to be examined. All the botanists except Boehm 

 agree that osmosis accounts for the absorption of the 

 w ater from the soil by the root-hairs, and for move- 

 ments of water in parenchyma generally: Boehm 

 refers the phenomena to differences of pressure, 

 rejecting other causes for the following reasons : 



(i) Osmosis acts so slowly. 



(2) The epidermis cells, from which transpiration 



^ ** Zur Theone dei Wasserbewegung m den Pflanzcn," jP;;//oi/^^zwV 

 Jahrh f Wtss. Bot. b xv. h 4, 1884., pp 569—630 



