HOW THE PLANT GROWS 



The sugars, which are the simplest of the carbohydrates, are all more 

 or less sweet in taste and are soluble in water. Because they are soluble, 

 they can be carried in solution in the sap of plants to all parts as needed. 

 Thus they are the portable, carbohydrate building material of plants. 

 Tho most plants store their reserve food in the form of starch, some plants 

 store sugar instead. 



The most common simple sugars found in plants are glucose, called 

 dextrose by the chemist, and fruit sugar, also called fructose or levulose. 

 These sugars have the formula, C 6 H 12 O e , there being 6 atoms of carbon 

 in each molecule. They are there- 

 fore called the 6-carbon sugars, or 

 hexoses. Both occur in the juices 

 of plants. 



Compound sugars are formed 

 in plants by the union of two mole- 

 cules of simple sugars and the 

 elimination of a molecule of water. 

 The most common is cane sugar, 

 or sucrose, which is made from 

 one molecule of glucose and one 

 of fruit sugar. Some plants, as 

 the beet and the sugar cane, store 

 their reserve food in the form of 

 cane sugar. Another compound 

 sugar, malt sugar, or maltose, is 

 formed by the union of two mole- 

 cules of glucose. Milk sugar, or 

 lactose, a third compound sugar ssoTtimes.) 

 of this class, is not found in plants but is one of the chief components of 

 milk. A compound sugar formed by the union of three molecules of 

 simple sugars is found in certain plants. 



Starch, one of the most important carbohydrates of plants, is in- 

 soluble in water and is formed by the union of many molecules of glucose, 

 with the elimination of water as a by-product. It is thus of much more 

 complex composition than the sugars. Most plants store their reserve 

 food chiefly as starch, which is deposited in the form of starch grains. 

 Starch therefore abounds in nearly all seeds, forming over 70 per ct. 

 of the dry matter in corn and wheat grains. Often starch is stored 

 in the underground parts of plants, as in the potato tuber, or in fruits, 

 as in the apple. Since starch is insoluble in the sap of plants, it must 

 be changed into sugars by an enzyme, or ferment, when it is needed in 

 other parts of the plant. For example, in a germinating seed the stored 

 starch is gradually changed into sugar, and this is carried to nourish 

 the various parts of the growing plantlet. (37) 



Cellulose, an insoluble, resistant carbohydrate of still more complex 

 nature than starch, is formed by the plant thru the union of a great 



FlG - 8. STARCH GRAINS 



