2 Bulletin of the University of Texas 



The process of photosynthesis easily ranks as one of the most 

 important of all vital processes, for upon it all life, animal as 

 well as plant, depends. All living substance requires for its nu- 

 trition, carbon, for it is one of the essential constituent elements 

 of such substance. But neither plants nor animals are able to 

 utilize crude carbon dioxide as food. It must first be combined 

 chemically with hydrogen to form sugar or starch before it can 

 be so utilized. It is seen, therefore, that plants and animals are 

 alike as regards their food requirements. They differ only as 

 to the manner of procuring food. The plant is an independent 

 organism which is able to manufacture its food from crude in- 

 organic material, while the animal is ultimately dependent upon 

 plants. 



It is a well known fact, that when materials containing carbon, 

 as for example, starch, oil, sugar, coal or wood, are burned, carbon 

 dioxide is given off and energy is released in the form of heat. 

 This heat energy was potential in the compound burned. The 

 radiant energy of sunlight enables the green leaf to unite carbon 

 dioxide and water to form carbohydrates, and becomes potential 

 in the compounds formed. Its subsequent release, to do our 

 bidding, depends upon the combustion of these compounds. The 

 energy which furnishes the chief driving power of the world's 

 machinery is energy from the sun, which has been arrested and 

 rendered potential by the green leaves of plants. The coal which 

 warms our homes, cooks our food, and drives our machinery, de- 

 pended for its formation upon this function of the leaves of 

 plants, which inhabited the earth at that remote age when 

 coal was formed. The heat energy has remained locked up, 

 potential in the carbon compound, awaiting an opportunity to 

 again become kinetic. 



The food substances which nourish plants and animals, fur- 

 nishing them materials out of which their bodies are built, and 

 energy with which to carry on their vital processes, depends 

 upon this ability of the green leaf to unite carbon dioxide and 

 water to form starch and store the radiant energy of the sun- 

 light in a potential form. The release of this energy by a liv- 

 ing plant or animal is accomplished by another vital process 

 known as respiration. 



If the ability of green leaves to carry on this most important 



