48 



BIOLOGY OF PLANTS. 



form water, (Symb. HO. eq.==9), a substance remarkable in its 

 relation to vegetation from the ease with which it is decompo- 

 sed, when subjected to the influence of the vital principle, as it 

 passes with great facility, through several transformations in the 

 vegetable organs. 



3. Carbon is the most abundant substance in vegetable bo- 

 dies. In its pure state, it exists as the most valued and beauti- 

 ful of gems — the diamond. Common charcoal is nearly pure 

 carbon. All kinds of coal are essentially composed of it ; great 

 quantities are also locked up in the rocks, in the form of car- 

 bonic acid, (fixed air). Common charcoal is a well known sub- 

 stance ; it burns with a white ligiit, but with little flame. As it 

 constitutes from 40 to 50 per cent, of all vegetables, it has much 

 to do in the processes of vegetation. One of its most impor- 

 tant properties is the power of absorbing several gases, a pro- 

 perty upon which its utility as a maniu-e depends. 



Carbonic acid. Carbon coml)ines with oxygen, and forms car- 

 bonic acid, or fixed air. This is a gaseous, transparent sub- 

 stance, two and a half times heavier than common air. It is 

 composed of one equivalent of carbon, 6.12, and two of oxTgen, 

 16 = 22.12. Its symbol is CO^. Carbonic acid is readily ab- 

 sorbed by water, to which it imparts a sour, lively taste ; also a 

 brisk, sparkling flavor to all fermented drinks, as beer. It is 

 sup{)osed to yield more carbon to plants than all other substan- 

 ces united. 



4. JViti'ogen exists in the atmosphere, of which it forms 80 per 

 cent. It is never absent from any part of the vegetable struc- 

 ture, but exists in small quantities. Animals contain larger 

 quantities of it. 



Nitrogen is a transparent gas, without color, odor or taste. 

 It is distinguished for its negative properties, for it will neither 

 support life nor combustion, but appears to act simply as a di- 

 luent to the oxygen of the atnjos{)here. Its compounds, how- 

 ever, are among the most active and useful substances. 



Nitric add, (NO^) commonly called aquafortis, is a com- 

 pound of nitrogen and oxygen. It exists both in the gaseous 

 and liquid state and is highly corrosive and active in its proper- 

 ties. In combination with potassa, forming nitre, and with other 

 alkalies, it is supposed to perform important offices in vegeta- 

 tion. 



Ammonia is well known as hartshorn. It is composed of ni- 

 trogen and hydrogen, (NIP) and exists as a gas, but is rapidly 



