CHAPTER III 

 PHOTOSYNTHESIS: GENERAL 



All flesh is grass. 

 — Isaiah 40:6. 



Plant Analyses. — If an ordinary green plant is placed in an oven, 

 it is found that a large percentage is water, which can thus be driven 

 off. Of the dry matter which is left after the water has been ex- 

 pelled, a certain percentage can be burned. This combustible por- 

 tion passes off in gases and smoke leaving a small incombustible 

 residue known as the ash. The mineral matter or ash is seldom 

 over 5% of the total plant, leaving 95% to be divided between 

 the water and the combustible materials, the proportions of which 

 vary in different types of plants as follows: 



Per cent 

 Plants Per cent water combustible matter 



Woody plants 40-50 55-45 



Herbs 65-75 30-20 



Succulents 80-90 15- 5 



Algse and water plants 85-95 10- 1 



Of the combustible dry matter, about 45% is carbon contained 

 in various carbon compounds within the plant. Organic chem- 

 istry, which now treats of carbon compounds, was called organic 

 chemistry because it was once thought that these carbon com- 

 pounds were formed only in living organisms. Since the days of 

 Wohler (1828), however, organic compounds have been synthe- 

 sized in the. laboratory in an ever-increasing variety and number. 

 Many are now synthesized and studied which have never been 

 found in plants or animals, so that the field of organic chemistry 

 is much larger than its name would indicate and the name has 

 hence become a misnomer. 



Source of Combustible Materials. — These organic compounds 

 made in the plant are manufactured from simpler inorganic ma- 

 terials, which the plant takes from its environment. These or- 

 ganic materials are then used by the plant in its life processes 

 and ultimately returned to the inorganic environment, either 

 during the lifetime of the plant or after it is dead, as the result of 



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