16 



Henry H. Dixon. 



Name 



Length of Stem 



Length killed 



Height attained 



Duration of 

 Expt. 



10-5 m 

 10-5 „ 

 12 „ 

 10-5 „ 



9 5 „ 

 10-5 „ 

 10-5 „ 



7 „ 



10-5 „ 



5 days 



5 ,. 



5 „ 



14 „ 



2 „ 



10 „ 



10 „ 



2 „ 



2 „ 



H .. 



The very structure of the conducting wood of trees, far from 

 supporting G o d 1 e w s k i 's contention that the cells assist in elevating 

 the transpiration stream, oifers the strongest evidence against it. 

 These cells, placed as they are beside the transmitting tubes, can by 

 their pumping actions in no way exert a lifting force on the stream. 

 The water, as experiment shows, is free to move downwards as well 

 as upwards. Nor would a polarized or unidirectional action of these 

 cells, as hypothecated by Janse^) help owing to their relation to 

 the tubes. In that case these cells would regularly draw in water 

 on one side and expel it on the other into tubes where it is exposed 

 both to downward forces and to resistance to upward motion. In 

 fact to utilize the pumping action of living cells in raising the 

 transpiration current would require that the continuity of the con- 

 ducting tracts should be here and there completely interrupted by 

 the pumping cells; but if flow he possible in permeable tissues round 

 these groups of cells, pumping actions on the part of the cells will 

 be futile in assisting to raise water. As is well known no such 

 interpolation of cells cutting the continuity of the woody tissues is 

 revealed by the most careful study of the conducting tracts. The 

 structure of the conducting tissues is, therefore, fatal alike to the 

 earlier views of Godlewski and Weste rmaier, and to the less 

 precise form under which they have been recently resuscitated by 

 Ursprung. 



The adhesion of writers to the vital hypothesis since Stras - 

 burger's results were published is so remarkable that we must 

 devote some space to examine fully the grounds for their contention. 



When a considerable length of a branch, still attached to an 

 uninjured plant, is killed by surrounding it with steam or hot water, 



1) J. M. Janse, Die Mitwirkung der Markstrahlen bei der Wasserbewegung 

 im Holz. Jahrb. f. Wiss. Bot., 18. 1887. 



