112 GLIMPSES IXTO PLAXT-LIFE 



In ordinary atmosphere there is a very small 

 quantity of a gas called carbon-dioxide.^ The 

 leaves absorb this gas from the air, and because 

 there is so little of it, each tree needs to spread out 

 an immense amount of foliage, that it may drink 

 in, by its means, all the carbon-dioxide that can 

 possibly be obtained. 



When this gas comes in contact with the 

 chlorophyll in a leaf, one part of the oxygen is set 

 free, and returns to the air in a pure condition, 

 thus making it more healthy for us to breathe ; 

 then the carbon and the remaining oxygen com- 

 bine with water in the leaf cells, and form starch, 

 the leaves retain the carbon, to build up their own 

 structure ; it enters indeed so largely into the 

 composition of vegetable substance, that in some 

 cases if we could burn one hundred parts of it, fifty 

 parts of the ashes would prove to be carbon or 

 charcoal. 



In a rough sort of way we may see for ourselves 

 how much carbon there is in woody fibre, b)- light- 

 ing an (ordinary wooden match and letting it burn 



' Carbon nieiining cliarcual, and iliuxidc uicaninL; two ]xirls 

 oxygen. Somelimes called carbonic-acid gas. 



