Leaves and their Work 175 



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 gradu- 

 ally burnt, 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 weight 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 without being able to extract any 

 from the air to feed upon, while the other had obtained 

 food enough for growing and breathing, too. 



There is some difference in the breathing of the 

 leaves and the blossoms of a plant. The blossoms 

 breathe faster than the leaves, especially when they are 

 just opening ; and they are therefore slightly warmer 

 in some cases, indeed, so warm that the heat may 

 actually be felt ! And the same is true of sprouting 

 seeds when there are many together. The sprouting 



