36 Public Parks. 



Fungi live upon decaying organic matter, and have not the power 

 of forming organizable products from inorganic material. 



We now come to that part of vegetable physiology in which we 

 are most interested. Under the influence of light, takes place the 

 chemical decomposition of one or more substances in the sap, 

 liberating the oxygen at the ordinary temperature of the air, 

 and transforming the mineral, inorganic food into organic matter — 

 the organized substance of living plants and animals. The chief 

 material given back to the air in this process is oxygen gas, that 

 element of our atmosphere which renders it fit for the breathing and 

 life of animals. That the foliage of plants in sunshine is continually 

 yielding oxygen to the surrounding air has been known since the 

 days of Ingenloup and Priestly. By exposing a few freshly- 

 gathered leaves to the sunshine, in a glass vessel filled with water, 

 air-bubbles will presently arise but cease to appear when placed in 

 the dark. 



There is no doubt but that all leafy plants obtain part of their car- 

 bonic acid from the air, for when a current of carbonic acid gas is 

 made slowly to traverse a glass globe containing a leafy plant exposed 

 to full sunshine, some carbonic acid disappears, and an equal bulk of 

 oxygen gas supplies its place. Carbonic acid gas contains just its 

 own bulk of oxygen. It is evident that what has thus been decom- 

 posed in the leaves, has returned all its oxygen to the air. Plants, 

 therefore, take carbonic acid, directly or indirectly ; they retain its 

 carbon, and give back its oxygen. 



Generally speaking, the plants may be said to be in a passive or 

 or state of rest at night, sometimes even throwing out carbonic acid 

 and consuming oxygen, and this is undoubtedly the reason why more 

 deaths occur at night, and the fatality incident to epidemics is 

 greatest. 



In fact vegetation is the only operation in nature which gives to 

 the air free oxygen which is indispensable to animal life, as all 

 animals consume oxygen at every moment of their life, giving to the 

 air carbonic acid in its room, and when dead their bodies consume a 

 further portion in decomposition, such being the case also with 

 vegetables. While animals consume the oxygen of the air, and give 

 back carbonic acid which is injurious to their life, this carbonic acid 

 is the principle element of the food of vegetables, is consumed and 

 decomposed by them, and its oxygen returned for the use of animals. 

 Hence the perfect adaptation of the two great kingdoms of living 



