164 THE PLANT PURIFYING THE AIR, [LESSON 26. 



pended or transferred from one part of the plant to another. In the 

 Sugar-cane and Indian Corn, starch is deposited in the seed ; in ger- 

 mination this is turned into sugar for the plantlet to begin its growth 

 with ; the growing plant produces more, and deposits some as starch 

 in the stalk ; just before blossoming, this is changed into sugar again, 

 and dissolved in the sap, to form and feed the flowers (which cannot, 

 like the leaves, create nourishment for themselves) ; and what is left 

 is deposited in the seed as starch again, with which to begin the 

 same operation in the next generation. 



471. We might enumerate other vegetable products of this class 

 (such as oil, acids, jelly, the pulp of fruits, &c.), and show how they 

 are formed out of the carbonic acid and water which the plant takes 

 in. But those already mentioned are sufficient. In producing any 

 of them, carbonic acid taken from the air is decomposed, its carbon 

 retained, and its oxygen given back to the air. That is to say, 



472. Plants purify the Air for Animals, by taking away the carbonic 

 acid injurious to them, continually poured into it by their breathing, 

 as well as by the burning of fuel and by decay, and restoring in its 

 place an equal bulk of life-sustaining oxygen (460). And by the 

 same operation, combining this carbon with the elements of water, 

 &c., and elaborating them into organic matter, especially into 

 starch, sugar, oil, and the like, 



473. Plants produce all the Food and Fabric of Animals, The herbiv- 

 orous animals feed directly upon vegetables ; and the carnivorous 

 feed upon the herbivorous. Neither the one nor the other originate 

 any organic matter. They take it all ready-made from plants, 

 altering the form and qualities more or less, and at length destroy- 

 ing or decomposing it. 



474. Starch, sugar, and oil, for example, form a large part of the 

 food of herbivorous animals and of man. When digested, they enter 

 into the blood ; any surplus may be stored up for a time in the form 

 of fat, being changed a little in its nature ; while the rest (and finally 

 the whole) is decomposed into carbonic acid and water, and exhaled 

 from the lungs in respiration ; in other words, is given back to the 

 air by the animal as the very same materials which the plant takes 

 from the air as its food (463) ; is given back to the air in the same 

 form that it would have been if the vegetable matter had been left 

 to decay where it grow, or if it had been set on fire and burned ; 

 and with the same result too as to the heat, the heat in this case. 

 producing and maintaining the proper temperature of the animal. 



