no GROWTH AND WORK OF PLANTS 



one molecule of sugar, therefore, 6 molecules of the carbonic 

 acid are necessary as will be seen by the following simple mathe- 

 matical formula, 6CO 2 +H 2 O=C 6 H 12 O 6 +6O 2 . There are 

 thus 6 molecules of pure oxygen set free in the plant cell which 

 the plant cannot use in this process. Much of this pure oxygen 

 escapes by way of the stomates into the open air again. It is 

 an interesting fact that during this process by which sugar is 

 made in plants, pure oxygen is added to the air and thus in 

 general the proper balance or proportion of this gas is maintained"; 

 otherwise, the air would in time become so depleted in oxygen 

 that it could not sustain animal life, since animals use oxygen 

 of the air in respiration. It is also interesting to note that, in 

 this process, the green plants use carbon dioxide from the air, 

 which animals give off during respiration. Green plants, there- 

 fore, in this respect, as well as in so many others, perform a very 

 important work in nature. 



174. How starch is formed from sugar.* Sugar is changed 

 to starch in the plant by the loss of one molecule of water. The 

 result can be seen from the following simple formula: Grape 

 sugar, C 6 H 12 O 6 H 2 O=C 6 H 10 O 5 ,f which is the symbol for 

 starch. In many plants the sugar formed in the leaves does not 

 change to starch except that which is stored in the seed, as in 

 field corn, wheat, barley, etc. Sugar is found throughout other 

 parts of the plant, and we have seen that it is stored in quantity in 

 the sugar beet. In some plants it is not even changed to starch 

 in the seed, as in the sweet corn. In many plants, however, it is 

 changed to starch in the leaf very soon after its formation in the 

 leaf, as in most dicotyledons. 



175. Where the starch grains are first formed. The sugar 

 is dissolved in the cell sap, but the starch is deposited in grains. 

 These grains of starch at the time of their formation are deposited 

 in the chlorophyll bodies. Each grain begins as a very small 

 body and increases in size. 



* For reference. 



j" The symbol for starch is probably some multiple of this and is usually 

 written (C 6 H 10 O 5 ) n . 



