84 THE MAKING OF THE LIVING MATTER 



may be the water forced up by the roots; some of it is 

 the condensed vapor of the air. 



176. TJie wilting of a plant is due to the loss of water 

 from the cells. The cell walls are soft, and collapse. A 

 grain bag will not stand alone, but it will stand when 

 filled with wheat. In the woody parts of the plant the 

 cell walls may be stiff enough to support themselves, even 

 though the cell is empty. Measure the contraction due to 

 wilting and drying by tracing a fresh leaf, and then trac- 

 ing the same leaf after it has been dried between papers. 

 The softer the leaf, the greater will be the contraction. 



Review. Whence comes the food of plants? "What is meant by 

 the dry substance? What is charcoal? How is it obtained? How 

 much of the dry substance is carbon? What becomes of it when 

 the plant is burned in air? Whence comes the carbon? What is 

 carbon dioxid? How abundant is it in the air? How does the C0 2 

 get into the leaf? What is chlorophyll? What function has it? 

 Where are the chlorophyll bodies located? What relation has light 

 to chlorophyll? W 7 hen is C0 2 absorbed? What is formed after C0 2 

 is taken in? Define photosynthesis. What is starch? What is 

 given off when starch is made by photosynthesis? In what part of 

 the plant is starch first made? When? What are carbohydrates ? 

 What is digestion of starch? How is the digested food distributed? 

 Explain assimilation. What is the product of assimilation? Explain 

 respiration. When are O and COo given off? Define transpiration. 

 Why do plants wilt? 



An egg-shell farm for the pupil's desk. 



