THE PLANT AS A WORKING MACHINE 151 



teins which it obtains from the plant. The green plant feeds 

 and lives on exactly the same compounds as. the animal, but, 

 unlike the animal, it must first manufacture these compounds 

 for itself from the water, carbon dioxide and mineral salts, as 

 will be explained in the succeeding chapter. Therefore, it will 

 be readily seen that the green plant is dependent on water, 

 carbon dioxide, character of soil, temperature and sunlight for 

 its existence ; but the animal is dependent upon the plant for its 

 existence. In brief, green plants take the water, carbon dioxide, 

 nitrogen and minerals which we may consider as crude or raw 

 foods and manufactures them into carbohydrates, fats, oils and 

 proteins, which we may consider as true foods ; both plants and 

 animals use the same compomids, carbohydrates, fats, oils and 

 proteins, for their growth ; animals and non-chlorophyll-bearing 

 plants, such as fungi (page 273), are dependent on the green 

 plants for their foods. The talcing in of raw or crude foods, the 

 manufacture of true foods, growth, waste, repair, reproduction 

 and behavior will be given consideration in following chapters. 



Gases, Liquids and Solids. — The crude foods are in the form 

 of gases, liquids and solids, and the true foods in the form of 

 liquids and solids. Therefore, it is necessary to know something 

 about the nature of these forms of matter. 



A gas is composed of very small particles which tend to sep- 

 arate indefinitely and if unoon£ned may become far separated 

 and intermingled with other gases. A gas may be dissolved in 

 another gas, in a liquid or in a solid. 



A liquid is composed of particles which are much less mobile 

 than those of the gases. It will shape itself to its container and 

 give off particles to the air as vapor. A liquid may be soluble 

 in another liquid. 



