LEAVES 383 



product which the leaves throw off. This will be seen in 

 Experiment 122. 



Experiment 122. Under an inverted funnel in a battery jar, 

 place some pond scum or horn wort. Fill the jar with fresh water 

 and over the neck of the funnel place an inverted test tube filled 

 with water. (Figure 122.) When placed in the sunlight, bubbles 

 of oxygen will rise into the test tube and collect. The 

 oxygen can be tested by turning the test tube right 

 side up and quickly inserting a glowing splinter. If 

 the splinter bursts into a flame, oxygen is present. (A 

 freshly picked leaf covered with water and put in the 

 sunlight will be seen to give off these bubbles.) After 

 a small amount of gas has been collected in the test 

 tube, mark the height of the water column and place 

 the battery jar in the dark, allowing it to remain there 

 for ten or twelve hours. No oxygen is given off in the dark. 

 Place the jar in the light again. Oxygen is given off. Is the sun's 

 energy needed to enable the plant to give off oxygen ? 



The starch manufactured is insoluble in water and is 

 stored in the leaf during the day. But at night, when 

 the leaf is not manufacturing starch, it is able to digest 

 the starch by means of a special substance, leaf diastase, 

 which it forms. This changes the starch into sugar, which 

 is soluble and which is carried in solution to other parts of 

 the plant. Compounds such as starch and sugar, in which 

 there are only carbon, hydrogen, and oxygen, are called 

 carbohydrates. 



The cells in the leaf and in other parts of the plant have 

 the power to change the sugar and combine it with- other 

 substances contained in the sap, thus forming more complex 

 chemical compounds. These contain nitrogen and sulphur, 

 besides the elements of the sugar. Such compounds are 

 called proteins. They are essential to the formation of 

 plant protoplasm and are very important as animal foods. 



