PROBLEM 67 85 



Problem 65 : To prove that water is given off by a green plant. 



Materials. — Bell jar, a growing single-stemmed green plant 

 as a geranium, rubber tissue, balance. 



Method 1. — Cover with rubber tissue a flower pot in which a 

 vigorous rubber plant or geranium is growing, so that only stem 

 and leaves are exposed. Water the plant prior to covering with 

 the rubber tissue. Then weigh the plant. Record weight. 

 Then re weigh the plant after two or three hours. 



Observations. — What difference in weight do you observe? 



Method 2. — Water the plant, tie up with rubber tissue as be- 

 fore, and place under a bell jar. 



Observations. — What collects on the inner surface of the jar? 



Conclusion. — 1. To what is the loss of weight due? 



2. How and when does the water get out of the plant? 



Note. — The giving off of water in the form of vapor through the leaves is 

 called transpiration. 



Problem 66 : Through which surface of a leaf does transpir- 

 ation take place ? 



Materials. — Two rubber-plant leaves, vaseline, scales. 



Method. — Cover the upper surface of one leaf and the lower 

 surface of the other with vaseline. Vaseline both leaf stalks at the 

 end where the leaves were broken off. Balance the leaves exactly 

 on the scales and place in a sunny place. 



Observations. — What happens? 



Conclusion. — Through which surface of a leaf does transpira- 

 tion take place? How do you know? 



Problem 67: To determine how the structure of a leaf fits it 

 for the work it has to do. 



Materials. — Entire leaf. 



Method and Observations. — Examine a leaf of maple or oak. 

 Notice that it consists of two parts : a stem, the petiole, and a broad 

 expanded part, the blade. Note, also, that the petiole leads into 

 a number of branching veins which support the blade. Estimate 

 the amount of green leaf surface in a plant in the room by multiply- 

 ing the surface area of one leaf by the number of leaves on the plant. 



