220 COLLEGE BOTANY 



into the proper light relationship. Also that potatoes which ger- 

 minate in darkened cellars produce long shoots which grow in the 

 direction of the light. Plants in the open are subject to the 

 same laws and the direction of stem growth and arrangement of 

 foliage is influenced by the direction and intensity of the sun- 

 light. The leaves on such vines as the Boston ivy and the grape 

 assume positions with reference to the sunlight. The leaves 

 on a tree are usually near the tip of the shoots and thus form 

 a canopy. Trees in dense forests tend to grow tall, because the 

 sides are shaded by other trees, while trees of the same species 

 in the open tend to produce broad, low, dense heads. The lower 

 branches of trees growing in dense forests die and fall largely 

 because they do not receive the necessary sunlight. 



LABORATORY EXERCISES. 



Exercise 1. Mix one gram of flour in 100 c.c. of H,0 and boil. Put 2 

 c.c. in each of ten test tubes. Add boiled diastase to two test tubes, and 

 fresh unboiled diastase to the other eight. Test two of the eight for 

 sugar immediately, two at the end of 30 minutes, two at the end of one 

 hour, and two at the end of 24 hours. Also test the two with the boiled 

 diastase at the end of 24 hours. 



Exercise 2. Translocation. Select active growing Geranium, Fuchsia 

 or other plants. Expose to bright sunlight for three or four hours. Re- 

 move two or three leaves; dissolve the chlorophyll and test for starch. 

 Set the plant in the dark for four or morei hours and test another set of 

 leaves in the same manner. 



