146 The Great World's Farm 



the soil; they cannot grow; but provided they have water, 

 why should they not remain as they were? What are 

 they doing to make them lose weight? 



Well, they are doing just what all living things do, and 

 must do, if they are to remain living; they are breath- 

 ing — breathing as animals do, though they have no lungs, 

 and though they breathe very much more slowly; that is 

 to say, they are taking in air. 



In breathing, as has been said, part of the oxygen of 

 the air inhaled combines with and burns up part of 

 the carbon taken in as food, converting it into the gas 

 carbon dioxide, which is breathed back into the air. 

 Warm-blooded animals breathe much more vigorously 

 than plants do, but the process is the same in both. 



Plants, however, breathe more or less through their 

 whole surface, though chiefly through their leaves, and 

 from the leaves, the air finds its way to every part. 



Probably the breathing of plants may be fairly com- 

 pared with the slow breathing of cold-blooded animals; 

 but though feeble it is always going on, night and day, in 

 light and in darkness, though more vigorously in light; 

 and therefore, as the stock of carbon is gradually burned 

 or oxidized, and breathed out, if it is not replenished it 

 must be gradually exhausted, and the plant must lose 

 weight. 



To prove this, two beans of nearly equal w^eight were 

 planted at the same time, one being kept in the dark, the 

 other in the light. At the end of twenty-six days it was 

 found that the seedling kept in darkness weighed more 

 than a third less than the original bean, and the other 

 weighed more than a third more. The one had breathed 

 away some of the carbon contained in the thick seed-leaves 



