THE DIFFERENTIATED PLANT 193 



tion to the two gases, oxygen and carbon dioxide. 

 This relation may best be investigated in the 

 germination of seeds, since there it is least 

 complicated by other processes. 



(1) Is oxygen necessary for the germination 



of seeds ? This can be answered by 

 an experiment in which a comparison 

 may be made between one set of 

 seeds supplied with oxygen, and an- 

 other set deprived of it. This has 

 been done in Experiment 3, in which 

 oxygen is left in the two tubes con- 

 taining the clear liquids, and absorbed 

 by pyrogallic acid and potash in the 

 other. Minutely observe this. 



(2) When one of these gases is absorbed, 



the other is usually given off. 

 Is carbon dioxide given off in growth ? 

 This may be answered by an experi- 

 ment in which a liquid capable of 

 absorbing carbon dioxide (such as 

 caustic potash) is so placed that it 

 will rise in a tube as it absorbs that 

 gas from a closed space. This has 

 been done in Experiment 3 in one of 

 the tubes containing the clear liquid. 

 The third tube contains simply water. 



(3) Is this process like anything in animals? 



