THE COMMON BEAN 13 



their radicles and push their way through the seed-coat even if 

 just kept above freezing point ; others require a temperature of 

 9° or 10° C. to start growth. If attempts are made to grow beans 

 at 45° C. it will be found to be too hot, and they make little or 

 no progress. Between this high temperature at which growth 

 appears impossible, and the freezing point where the develop- 

 ment of the embryo of the bean is also suspended, there is a 

 temperature at which the embryo makes the most rapid progress, 

 and emerges from the seed-coat in the shortest possible time ; 

 this most favourable temperature is about 28° C, both above it 

 and below it the germination of the bean is retarded. 



Ex. 6.— Arrange two separate lots of similar-sized beans soaked for the 

 same length of time in damp flannel as described in Ex. 3, and place one 

 in a warm kitchen and the other in a cold cellar. Observe which show 

 their radicles first. 



5. The supply of fresh air is also an essential condition for growth 

 of the young plant from the bean seed, but the evidence for its 

 need is not so manifest or so generally recognised as the necessity 

 for moisture and warmth. It will be found, however, when 

 beans are placed in a flask or bottle containing carbon dioxide or 

 hydrogen gas they refuse to germinate, even when they are sup- 

 plied with a proper amount of water, and kept at summer heat. 



Ex. 6. — Place ten soaked beans in a wide-necked bottle. Fill the bottle 

 with carbon dioxide gas or coal gas, and cork it up with a tightly-fitting 

 indiarubber stopper. 



Arrange another bottle in the same way, but with ordinary air in it instead. 

 Take out the stopper of this one twice daily and blow in fresh air, so as to 

 ensure a good supply to the seeds. Place both in a warm situation and 

 observe which germinate best. 



6. The peculiar extension or growth of the parts of the interior 

 of the bean seed, and the fact that a suitable supply of water, air 

 and heat is necessary for the manifestation of these changes, 

 suggests to us that we are dealing with a living structure. This 

 becomes all the more apparent when we observe that the oxygen 



