IQ02] RISE OF THE TRANSPIRATION STREAM i8l 



m this form. The inibibitionists never offered any physical 

 explanation of the supposed absence of high friction in the fine 

 pores of the wood; this was dismissed as a "natural property*' 

 of the wood substance. 



The imbibition theory fell with the disproof of its first 

 premise, that the water moved in the walls. Unger's injection 

 experiment was repeated with the opposite result.' Elfving- 

 (1882714) plugged the lumina of pieces of wood with cocoa 

 butter and could force no water through them. Scheit (1884) 

 injected sticks with gelatin with the same result. Vesque 

 (1884:188) injected the tracheae of a living branch with cocoa 

 butter and the branch wilted. Errera (1886J, 31,11) repeated 



this experiment using gelatin ; as did also Strasburger (1891 :540- 

 Dixon and Joly (1895) employed gelatin, paraffin, ice, and water 

 vapor to obstruct the lumina, causing wilting in each case. 

 Smith found the movement of water in cucumber stopped or very 

 nearly so by injection with gelatin; the plugging of the spiral 

 vessels by Bacillus tracheiphihts caused a gradual wilting, while 

 Fusarium niveiim, which fills the pitted vessels as well, causes a 

 sudden collapse of watermelon foliage. Vesque (1884), Kohl 

 (1885), and Darwin and Phillips (1885:366) made plants wilt, 

 or checked the absorption as measured by the potometer, by 

 squeezing them until the lumina were presumably closed. The 

 old observation (DeVries) that if a transpiring branch is cut in 

 the air it wilts was recognized as showing that plugging the 

 lumina with air closed the path of the water (Scheit, 1886:172). 

 Against the experiments with bent branches it was pointed out 

 by Russow (1883:99) and Scheit (1884) that bending does net 

 entirely close the lumina. And Dufour's inability to force 

 water through the bends under pressure was ascribed by the 

 opponents of his theory to the entrance of air where his wood 

 was exposed in cutting. 



The movement of w^ater in the lumina was directly observed 

 by a number of investigators, notably Vesque. The well-known 

 presence in the lumina of colors and other substances used in 

 detecting the path of the transpiration stream had been ascribed 



