76 MASSACHUSETTS AGRICULTURE. 



plants ; that it is insoluble in water and even in the strongest 

 acids or alkalies. How then came it in the plant which we have 

 seen has no power of taking up substances in the solid state ? 

 Place your charcoal on the fire, and it mostly disappears. Is it 

 annihilated ? No. Man can destroy nothing. It has united 

 with oxygen the vital part of the atmosphere, and formed an 

 invisible gas, which in its behavior is wholly unlike either 

 charcoal or atmosphere. It is not solid. Heat it and it will 

 not burn ; thrust a candle into it and the candle goes out ; 

 breathe it and it kills you. Chemists have called it carbonic 

 acid. It is composed, by weight, of six parts charcoal and 

 sixteen parts oxygen. From four to six parts in each ten 

 thousand of the atmosphere is carbonic acid. The falling 

 rain absorbs it, the spongioles take it up, it is transported 

 to the leaf, and there comes in contact with the chlorophyl. 

 When the sun shines upon it, the sixteen p*^rts of oxygen are 

 liberated, given back to the atmosphere, and the charcoal is 

 combined with the water, making woody fibres. Immerse a 

 growing plant in the water and place it in the sunshine, and you 

 will see little bubbles rising from the leaves. Invert a tumbler 

 over it — you may catch the bubbles as they rise. When the 

 tumbler is full, place a candle in it and it burns with great 

 brilliancy, breathe it and it is a tonic. It is not carbonic acid, 

 it is pure oxygen. 



The leaf also absorbs much carbonic acid directly from the 

 air and some plants derive most of their carbon in that way. 

 Place a growing plant under a receiver full of carbonic acid and 

 common air ; by and by it will be found that the carbonic acid 

 has gone, and oxygen has taken its place. 



Every fire that burns, every animal that breathes, sends out 

 carbonic acid to feed the plant, and every plant is at work 

 decomposing the gas and returning the pure oxygen to the air 

 for the consumption of the animal. Deity has made these 

 kingdoms complements of each other — parts of the united whole. 



There is an element of food for the plant which deserves 

 passing notice here. It is small in quantity but seems as essen- 

 tial to the plant as nails to the house. Its name is nitrogen. 

 It exists only in the new cells, never in the old. It exists also 

 in the gluten of wheat and in peas and beans. There is a little 

 about each eye of the potato and in the germ of every seed. 



