134 



THE LIFE OF THE PLANT 



the globe, while still connected with the vine, and 

 therefore under perfectly natural conditions. With 

 the help of an aspirator a continual stream of fresh 

 external air, as is shown by the arrows on the figure, is 

 slowly passed, first through the glass bell and then 

 through the apparatus A connected with it. We mark 

 on the aspirator the volume of air passed through 

 the globe during the experiment ; we also analyse the 

 air of the place where the experiment is made, and 



FIG. 39. 



determine the proportion of carbonic acid contained 

 in it. When once we know the amount of air which has 

 been passed through the globe containing the plant, and 

 the proportion of carbonic acid contained in the air, we 

 can easily determine the quantity of carbonic acid that 

 has entered it. We have now only to determine the 

 quantity of carbonic acid that has come out of the globe 

 in order to find out how much of it has been decom- 

 posed by the leaves. The apparatus A serves this 

 purpose. I will briefly describe its significance, again 

 leaving out all technical details, since my point is merely 

 to explain the fundamental idea of the experiment and 



