SEED GERMINATION 



69 



We have already proved in Exercise 20 that germinating 

 seeds take in oxygen. Now what do they give off in 

 exchange for this? 



EXERCISE 22 



Object. — To prove that a germinating seed 

 gives off carbon dioxide. 



Procedure. — Secure a piece of fresh unslaked, 

 or unslacked, lime about a third as large as an 

 egg, and slake, or slack it by putting it into a 

 quart jar or can of water. Allow it to stand 

 for two or three hours, and pour the 

 liquid into a clean bottle through a 

 piece of filter paper; or if the liquid 

 is perfectly clear, it is unnecessary to 

 filter it. You now have 

 clear limewater, which 

 should be tightly 

 corked if not used 

 at once, as it reacts 

 with the carbon di- 

 oxide of the air. 



Place a small 

 amount of this water 

 in a second bottle and blow into it through a small paper 

 or glass tube. As the bubbles pass through it, the lime- 

 water will turn milky, due to the fact that the carbon 

 dioxide from your lungs unites with the lime dissolved 

 in the water, forming innumerable, minute pieces of lime- 

 stone, which will not dissolve in the water but which will 

 finally settle.' This is the test for carbon dioxide. It 

 will turn limewater milky, and no other gas will do so. 



' Limewater contains slaked lime. This consists of calcium 

 oxide, CaO, combined chemically with water, H2O. When 



ABC 



Fig. 20. — Seeds germinating at difEer- 

 ent temperatures. C has germinated at 

 the optimum temperature, B and A .at 

 10° and 20° C, respectively, below optimum. 



