76 



THE LIFE OF THE PLANT 



plays over the surface of the seeds, and then passes 

 through the Hquid in the funnels b and b'. You notice 

 already the difference which manifests itself : while the 

 liquid maintains its transparency in the left funnel, it 

 becomes turbid and turns milky white in the right one, 

 and within a short time a considerable layer of chalk is 

 precipitated. Evidently air after passing over a layer of 

 living, germinating seeds contains carbonic acid. Seeds, 

 therefore, absorb oxygen and give off carbonic acid. 

 We have now to show that these two processes are 

 correlated, i.e. that carbonic acid is given off in place of 



oxygen which has been absorbed. 

 This can be demonstrated by the 

 following experiment, which at 

 the same time allows us to judge 

 of the energy with which this 

 process of respiration proceeds. 

 A narrow glass bell a (fig. 23) 

 is divided into two parts by 

 wire gauze ; some germinating 

 hemp seeds are scattered in the 

 upper part, while in the lower, 

 which is closed with an india- 

 rubber stopper, a small beaker 

 is placed containing a solution 

 of caustic alkali. The upper 

 aperture of the bell is likewise 

 corked with an india-rubber 

 stopper through which passes a 

 bent manometric tube containing 

 a column of coloured liquid and 

 provided at b with a stop-cock. 

 This stop-cock is open for the pur- 

 pose of keeping the air inside and outside the apparatus 

 in equilibrium. Whenever this stop-cock is closed the 

 column of coloured liquid rises in the left limb of the 

 manometer and falls in the right one, so that its level will 



Fig. 23. 



