122 PLANT PHYSIOLOGY 



or less modified form by a number of other authors. Accord- 

 ing to this view, the living cells which are always found to 

 be the close neighbors of ducts and tracheids participate 

 actively in raising water from roots to leaves. Apart from 

 the anatomical relationship of these living and lifeless ele- 

 ments, which suggests that the living cells may aid in as 

 well as influence the movement in the lifeless ducts and 

 tracheids, it is definitely proved by experiment that it is the 

 youngest wood, that is, the wood containing the most and 

 the most active living cells, which transfers most water and 

 does it most rapidly. The method of proof consists in using 

 solutions of harmless coloring-matters not fixed by living 

 cells ( e. g. Indigo-carmin, Anilin Blue, etc. ) . If amputated 

 branches are placed in such solutions the path of transfer 

 will be indicated by the staining of cell-walls, and if the ex- 

 periment is not prolonged, the stain will be found highest 

 in the youngest, that is, the best-conducting wood. The 

 "sap-wood" conducts most if not all of the water. On the 

 other hand, the "heart- wood " conducts little or none. The 

 heart-wood not only contains fewer living cells — the oldest 

 heart-wood none at all — but its permeability diminishes as 

 the infiltration of the walls with coloring, hardening, pre- 

 serving, and other substances progresses. In the youngest 

 wood, where there are the most living cells, the maximum 

 transfer of water takes place. 



Against the idea that living cells are actively concerned in 

 raising water from root to leaf are the conclusions drawn 

 by Strasburger from his experiments. The following will 

 serve as an illustration of one line along which he experi- 

 mented.* A specimen of Acer platanoides twenty-one metres 

 high was obliquely sawed through at the base, a strong 

 stream of water playing constantly into the cut as the saw- 

 ing progressed. The tree was then placed with the butt in 

 water. After the lapse of a half-hour it was hoisted, the 

 cut surface smoothed with a sharp knife, and then lowered 

 into a 5% solution of copper sulphate. In two weeks it took 

 up nearly 30 litres of this liquid and the presence of the 

 copper could be demonstrated up to, but not in the finest 

 * Strasburger, E. Bau und Verrlchtung der Leitungsbahnen, p. 617, 1891. 



