iv.] VARIOUS THEORIES, &c. 137 



are indispensable for the ascent of the water in the 

 wood. 



In 1886 Leo Errera opened up once more the 

 question of Elfving's experiments, 1 and their critics, 

 and disposed of the latter by using gelatine (as 

 Scheit had done) to stop up the cavities of the ele- 

 ments, and by employing the transpiration-current 

 itself i.e. using cut branches with their foliage on. 

 Hence he confuted the objection that Elfving had 

 only proved the case for filtration under pressures. 



Branches were used (i) cut under water, so as to 

 inject the vessels with water ; (2) cut in air, and the 

 vessels therefore largely filled with air ; (3) cut under 

 liquid gelatine, so as to stop up the lumina when the 

 gelatine congealed. The surfaces were then cut 

 clean, and the three sets of branches, in water, exposed 

 to transpiration. 



It was found that those blocked with gelatine 

 drooped at once, but recovered if cut higher up ; 

 whereas the others transpired normally. 



Errera also adds a critical note derived from 

 Sachs's own statements ; the latter says, 2 that the 

 thick walled and dense autumnal wood of each 



1 L. Errera, " Ein Transpiration Versuch," Her. d. Dentsch. Bot. 

 Gesellsch., 1886, p. 16. 

 8 Varies, iiber p. Physiologic, p. 275. 



