166 KESPIRATION. [CH. VII 



(195) Noll's experiment^. 



Noll's method is to fix a grass-haulm into a glass tube 

 so narrow that it only just fits, and to leave it horizontal 

 in damp air. The pulvinus cannot curve, but the lower 

 half of the pulvinus grows out into curious excres- 

 cences. We arrange the experiment differently. Cut 

 a groove in a block of cork about 5 mm. wide and 

 5 deep. Arrange 3 or 4 grass stalks on the cork so that 

 they lie across the groove with the pulvinus of each over 

 the groove. Fix them in place by two sheets of cork, one 

 of which pins down the stalks on one side of the groove, 

 while the second sheet fixes the parts of the stalks on the 

 opposite side. The whole arrangement is put in a tin 

 box half-full of wet sawdust for 5 or 6 days, when the 

 result should be clear. 



(196) Fi^ee oxygen necessary. 



The bean, which should have a short root (15 mm.), is 

 pinned in the vertical position to the lower surface of a 

 rubber cork fitting tightly into the ground neck of a 

 small bottle. Hydrogen is passed through the bottle for 

 about 2 hours to replace the contained air. The bottle is 

 then placed on its side so that the root is horizontal. 

 The tube connecting with the hydrogen-generator is kept 

 open while the outflow tube by which the hydrogen 

 current escaped from the bottle is shut ; in consequence 

 of this arrangement the only leakage that can occur is an 

 escape of hydrogen. After 24 hours, during which no 



1 Sachs' Arbeiten, iii. p. 509. 



