

I 



1902] RISE OF THE TRANSPIRATION STREAM 177 



Acacia as rapid as that of the transpiration stream. Too much 

 air in wood hinders or prevents the movement of water, as 

 proven by Boucherie and many of his successors. It is for this 

 reason that shoots cut in air wilt though the cut end be after- 

 wards placed in water ; the lesser tension in the tracheae caus- 

 ing those exposed to fill with air at the outside tension. On the 

 other hand, when the vessels are well supplied with water, the 

 removal of part of it facilitates its movement in response to the 

 '^attraction " above — according to Dutrochet. It is my belief 

 that in lofty trees it would be impossible for water to be drawn 

 from the root while the tracheae are even approximately full of 

 it; though of course all that is certain or can be demonstrated 

 empirically is that there is a great deal of space occupied by gas 

 when transpiration is rapid. 



In a capillary tube filled with a succession of bubbles of air 

 separated by water (Jamin's chain), the resistance to the move- 

 ment of the entire column of air and water is very considerable 



(J 



Steinbrinck). While measurements 



made in glass tubes are not valid for the tracheae (Strasburger, 

 1891 :8i5), the movement of the bubbles in the latter is inter- 



■ 



fered with by the sculpturing of the walls and the remains of 

 the partitions (Kamerling, 1898, I: 978). The result is that a 

 pressure insufficient to move the bubbles will cause a flow of 

 water between the bubbles and the wall. 



Vesque (18S2; Ann. Sc. Nat. 1883) and Capus observed 

 under the microscope that bubbles did not prevent a current 

 above and below them in the same vessel. Vesque [cf. 1891 : 

 384 ; the original publication was in the Annalcs Agrommiques 

 II : 1885) afterward determined that this current passed between 

 the bubble and the wall ; which was confirmed by Strasburger 

 (1891 -.701). Pappenheim (1892: 161) was unable to demon- 

 strate such a movement ; nor could Schwendener, who denied its 

 possibility (1886; 1892:920). I have not found Vesque's 

 experiments exceedingly difficult, either in glass tubes or in 

 tracheae, and will describe some of them briefly later in this 

 paper. The same phenomenon can be conveniently observed in 



