36 HORTICULTURE FOR SCHOOLS 



Examine the marked parts from time -to time to see where the marks 

 are farthest apart. Which are the most rapidly growing portions in 

 each case? 



2. Materials, Trees with growing shoots; labels. 



Procedure. (a) As early in the growing season as possible, select 

 and label a growing shoot on any convenient tree. Make a drawing 

 of the shoot showing nodes and internodes. Measure the length of the 

 internodes and record the results on your drawing. Repeat the measure- 

 ments every two weeks. Report the results, (b) Proceed in the same 

 way with a branch two years or more of age on the same tree. Do the 

 internodes lengthen? (c) What bearing have the facts learned in this 

 exercise on pruning and forcing the height of head of a young tree? 



EXERCISE III. Exercise to show the presence of water in plant 

 tissues. 



Materials. Cans or evaporating dishes; small scales; leaves; twigs 

 from a tree; oven. 



Procedure. (a) Weigh out some fresh leaves in cans or evaporating 

 dishes. Record the weights. Dry the leaves in an oven for a number 

 of hours, at a temperature of about 212 degrees F. Then weigh the leaves 

 again. The difference in weight is due to the loss of water. Compute 

 the percentage of water contained in the leaves. Compare your results 

 with those of others in the class, (b) Repeat the experiment with young 

 twigs cut into small pieces. Obtain the percentage of water. 



EXERCISE IV. Exercise to illustrate osmosis or the way in which 

 root-hairs absorb moisture. 



Materials. Thistle-tube; stand and clamp for holding thistle- tube ; 

 parchment paper or pig's bladder; molasses or sugar solution; beaker 

 of water. 



Procedure. Perform the experiment described in paragraph 39. 



EXERCISE V. Exercise to show that the epidermis prevents unneces- 

 sary evaporation of moisture. 



Materials. Geranium stems. 



Procedure. Divide the stems into two portions. After removing 

 the leaves, peel the outer tissue (bark) from one portion. Weigh each 

 portion separately. Place both portions in the sun and after a time 

 weigh again. Note the difference in loss of moisture. (The same 

 experiment may be done with fruits of the apple, pear, or orange.) 



