MANUAL OF GENERAL AGEICULTURE. 51 



In the case of the potato the piece in water is plump 

 and rigid, which shows that the water passed into the 

 potato faster than the sap passed out. The piece in the 

 salt solution is wilted, which shows that the salt solution 

 did not pass into the potato as fast as the sap passed out. 



In the case of the egg, the water passed into the 

 egg more readily than the denser egg solution passed out 

 into the water. As the water passed in, the egg albumen 

 was pushed up the tube by osmosis. Whenever a plant or 

 an animal membrane separates two solutions, there is an 

 interchange of the two. The less dense the solution, the 

 more rapidly the water passes through the membrane. The 

 solutions of root-hairs are more dense than the soil solu- 

 tions, hence more water passes into the root than passes 

 out into the soil. 



Questions: I. What is the danger in using an ex- 

 tremely strong fertilizer? 2. How does this experiment 

 show that an excess of alkali in the soil often prevents 

 the growth of the plant? 



52. THE WORK OF LEAVES. 



Materials: Two small watch glasses, vaseline, two 

 circular disks of two pins. 



1. Transpiration. Fasten two small watch glasses, 

 one on each side of a leaf of a plant growing vigorously 

 out of doors. The glasses may be held in place by sealing 

 the margin of each all the way around by vaseline or 

 grafting wax. An hour later or at the next meeting exam- 

 ine the drops of water inside of each glass. The giving 

 off of moisture by the leaves is called transpiration. 



2. Light. Select some leaves on a vigorously grow- 

 ing plant. Shut off the sunlight from parts of the selected 

 leaves, which must be left on the plant and as little injured 

 as possible, by pinning circular disks of cork loosely on 

 opposite sides of each leaf. Two or three days later remove 

 these leaves and the cork disks. Compare the color of the 

 covered area with the color of the remainder of the leaf 

 and explain. Why do most plants not do well in the 

 shade of trees? 



