168 COLLEGE BOTANY 



ence on the soil; the humus of the soil, which is so important 

 in plant growth, is recognized as coming from the decay of 

 organic materials. However, it is also well known that both 

 living and decaying plants produce compounds which are in- 

 jurious to plant growth; therefore, it is frequently necessary 

 to give the soil mechanical and chemical treatments, or to allow 

 it to remain idle for a time, or to practice the rotation of crops 

 in order to maintain a maximum production. 



LABORATORY EXERCISES. 



Exercise 1. Chop 10, 50 or 100 grama of lettuce or cabbage leaves. 

 Weigh carefully. Dry thoroughly in an oven at a temperature of about 

 100 degrees C. Weigh and compute loss in water. Repeat this experi- 

 ment, using twigs, fruits and seeds of various kinds. 



Exercise 2. Grow several plants in unperforated glass or porcelain 

 containers filled with soil of the same kind. When well started, insert 

 the stem of a funnel into the soil and cover the surface of the soil with a 

 soft wax composed of a mixture of paraffin and vaseline. Water the plants 

 through the funnels from day to day, using different amounts of water for 

 each plant. Note the effect on growth. 



Exercise 3. Note plants growing in the open. What plants grow in 

 the water, in swamps and on dry land? 



Exercise 4- Review your studies of the root-hair (Chapter IV). 



Exercise 5. Place a few root-hairs on a slide in methylene blue and 

 observe under the microscope. Note the penetration of the color. 



Exercise 6. Examine and compare two or three types of soil under 

 the microscope. 



Exercise 7. Fill glass tubes about two feet in length and about one- 

 half inch in diameter with soil of various types, and stand in water. Note 

 the rise of the water. 



Exercisd 8. Dry definite amounts of two or three types of soil thor- 

 oughly; add definite amounts of water and expose in open vessels for a 

 few hours. Weigh and compute the relative water losses. 



Exercise 9. Pull seedlings that have been grown in loose soil and 

 examine the root-hairs under the microscope. Note the relationship to the 

 soil particles. 



Exercise 10. Grow seedlings of the same kind in soil of the same type 

 in two four-inch pots. When the seedlings have several leaves, quit 

 watering one lot. When wilting begins, determine percentage of water in 

 the soil. 



Exercise 11. Place living shoots of Elodea or similar water plants or 

 living algae in about 1000 times their volume of .01 per cent, solution of 

 methylene blue for about 24 hours. Examine for color. When the color 

 is noticeable, plasmolyze the cells with potassium nitrate solution. 



Exercise 12. Cut cubes of soft, dry wood, measure carefully and soak 

 in water for several days. Measure again. The water should be changed 

 every day. 



