96 Plants and their Ways in South Africa 



o 



dioxide, the gas that was breathed from the lungs, is required by the plant 



to combine with water to make starch. 



Ex. 4 t. What gas is given off when starch is made? Place a 



glass funnel over the plants in the jar, with the small end under water. 

 Sink a test-tube into the water obliquely, so 

 that all the air may escape and the tube 

 fill with water. Without letting the open 

 end come above water, place it over the 

 small end of the funnel. As the gas rises 

 it drives out the water. When the tube is 

 full, light a long splinter, and blow out the 

 flame, leaving the end glowing. Quickly 

 lift the tube from the water and thrust in 

 the glowing splinter, which again bursts 

 into flame. We know from the last chapter 

 that oxygen is the gas necessary to light 

 a fire. 



Ex. 42. To show that no Starch is 

 made without Carbon Dioxide. Cut 

 under water two small shoots and place in 

 small vials of water. Lower the vials into 

 wide-necked jars and tie over the mouths 

 of each some cloth net. Sprinkle over one 

 net a thick layer of soda-lime ; over the 

 other a layer of sand. In a day or two 

 the plant under the soda-lime withers and 

 droops. A test for starch shows that none 

 has been made. The covering of soda- 

 lime absorbs the CO 2 and prevents any 

 from entering. Carbon dioxide was ad- 

 mitted into the one covered simply with 



S 



FIG. 81. E, Elodea plants 

 in water, with the cut ends 

 of the stalks directed into 

 the glass funnel, F ; S, sup- 

 ports on which the funnel 

 rests ; T, test - tube ; O, 

 oxygen which has collected 

 in the test-tube. (From 

 Farmer's " Practical Intro- 

 duction to the Study of 

 Botany".) 



sand, and starch-making was unhindered. 



In making starch, plants give off the gas we require in 

 breathing. 



In respiring, plants and animals exhale the gas which 

 plants require for starch- making, carbon dioxide. 



Assimilation requires light. Respiration takes place 

 in darkness as well as in the light. 



Assimilation takes place in green parts. Respiration 

 in all parts of the plant. 



Assimilation builds up material and increases the weight of 

 the plant. Respiration breaks down material and the 

 plant loses in weight. 



