THE SPERMAPHYTES. 245 



the volume of the water in the tube is diminished, and the 

 mercury rises into the tube. 



25. Show that the presence of sunlight is necessary for 

 the healthy development of plants. 



a. Place plants that are growing healthily in a dark 

 room. Keep all other conditions favorable. Examine at 

 intervals for several weeks. Do they continue healthy? 

 Do they grow more or less rapidly than in the light? 



b. Weigh each of a number of Peas and Beans. Ger- 

 minate them, using Sachs' food solution. After they are 

 well started keep one half in the sunlight and the other 

 half in the dark, all other conditions being alike and 

 favorable. After three or four weeks remove the seed- 

 lings, rinse in water, and dry for a week at the ordinary 

 temperature and protected from dust. How do the 

 weights compare with the original weights of the seeds? 

 What conclusion do you draw from the experiment? 



c. Cut transverse sections of leaves that grow in the 

 bright sunlight and of those that grow in the dense shade 

 of the interior of a thickly leaved tree. Leaves of Beech 

 are good. Compare the palisade parenchyma produced 

 under the different conditions. What conclusion do you 

 draw ? 



26. Study the movement of the nutrient fluids. 



a. Girdle a young tree by removing the bark and the 

 youngest layer of wood. The tree continues to live for 

 some months. This proves that the nutrient fluids ascend 

 in the older wood, and not in the bark portions. The tree 

 dies before the second season. This proves that the 

 nutrient fluids, elaborated into foods in the leaves and 

 other portions of the plant, could not descend to nourish 

 the roots, and there to be stored up for future growth 

 of the plant. These fluids must therefore descend in the 

 bark portions of the plant. 



b. Place the cut end of a Geranium stem in a solution 



