106 CHEMICAL COMPOSITION OF THE PLANT 



wood. But when the fragment of charcoal is burned we have a 

 few ashes remaining. The chemist tells us that this ash contains 

 small quantities of phosphorus, potassium, calcium, mag- 

 nesium, sulphur, sodium, chlorine, manganese, aluminum, etc. 

 The water, carbon and nitrogen which we know make up a con- 

 siderable part of the plant have been carried off as vapor and 

 gas during the process of burning. 



The water is composed of two gaseous elements, hydrogen 

 and oxygen. When wood burns or decays, the carbon (C) unites 

 with the oxygen (O) of the air forming a gaseous compound 

 known as carbon dioxide (CO 2 ), which is available for new 

 plant growth. (Page 115.) 



Starch. We also know that plants contain starch which is 

 composed of three elements, carbon, hydrogen and oxygen, com- 

 bined as C 6 H 10 O 5 . Starch is one of the most abundant plant 

 substances and is one of the valuable plant products of com- 

 merce. It constitutes a considerable part of the dry substance 

 of seeds, green fruits, fleshy roots, tubers, bulbs, fleshy leaves, 

 etc., in which it can be readily detected by very simple experi- 

 ments. Starch is one of the important food substances for both 

 man and beast. Potatoes, sweet potatoes and other tubers and 

 fleshy roots contain large quantities of starch. Grains, peas, 

 beans and other seeds contain an abundance of starch. The 

 starch not only makes these plants valuable for food but also for 

 other purposes. Tapioca, some forms of paste and other ar- 

 ticles of commerce are made from starch. The following table 

 shows the relative amount of starch found in some common food 

 plants, as estimated in percentage of dry weight. 



Plant products Percentage of starch 



Seeds of navy beans 45 



Seeds of peas 52 



Seeds of corn 60 



Seeds of wheat 68 



Seeds of rice 68 



Tubers of potatoes 80 



