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 erude 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- 
hght 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 
