ABSORPTION OF GASES. 83 



is greater than could be accounted for by the absorption of 

 carbon dioxide from the air, and that therefore some other 

 source of supply of carbon probably the carbon dioxide 

 absorbed by the roots must be assumed. Recent investiga- 

 tions have, however, shewn that this theory is quite untenable. 

 Bohm has found that a plant cannot live long when its leaves 

 are enclosed in a receiver containing air from which all car- 

 bon dioxide has been removed, even although its roots are 

 in soil rich in humus and therefore also in carbon dioxide ; 

 and Moll has come to the conclusion that the carbon dioxide, 

 which may be present in one part of a plant does not contri- 

 bute to the formation of starch in the chlorophyll-corpuscles 

 of another part. We are therefore justified in holding the 

 opinion that the carbon dioxide which a plant requires is 

 absorbed from the air by those of its organs which contain 

 chlorophyll. 



Figures illustrating Moll's experiments. 



FIG. 17. The glass jar covering the left-hand plant stands in a dish (6) contain- 

 ing solution of potash, and its contents communicate with the air by means of 



62 



