The question as to what becomes of all the roots, and why the 



to some of us. Several causes explain this, one of which is the 

 process of putrefaction, which is explained by the respiration of 

 a certain kind of microscopic plants. These plants are called 

 anaerobes, because they normally respire anaerobically, that is, 

 without the presence of free external oxygen. Some of them 

 are unable to respire at all if free oxygen surrounds them. If, 

 therefore, the aeration of the soil is interfered with, these plants 

 find ideal conditions for their growth and activity, and the soil 

 becomes " sour," and unfit for crops. 



From the above considerations it becomes clear that agricul- 

 ture, the most fundamental of all human industries, depends for 



the fact that plants respire. 



But husbandry is not the only point where the respiration of 

 plants touches our daily lives. Upon the respiration of the yeast- 

 other countries, and upon the respiration of another yeast-plant 

 we are dependent for the lightness of our daily bread, for the 

 fermentation involved in " raising " dough is a kind of respiration. 

 The difference between a " good " and a " bad " cigar is partly 

 attributable to a similar cause, for the difference is connected 

 with the curing of the tobacco, and this process involves the 

 respiration of bacteria. So, too, does the tanning of hides, and 

 the separation of flax and hemp fibers from the plants that pro- 

 duce them. 



sary, in part, because of the respiration and universal presence 

 of myriads of microscopic plants that float in the air, for, whereas 

 heat accelerates respiration, cold retards it. The turning rancid 

 of butter, the souring of milk, the formation of vinegar from 

 cider, are all dependent upon the same process. If plants did 

 not respire canned fruits and meat would seldom spoil. That 



