:62 STRUCTURE AND PHYSIOLOGY OF SEED PLANTS 



Transfer each plant to a glass battery jar of suitable size. Cover the jar 

 with a piece of thin sheet lead, slit to admit the stem of the plant, invert 

 the jar, and seal the lead to the glass with a hot mixture of beeswax and 

 rosin. Seal up the slit and the opening about the stem with grafting wax.i 

 A thistle tube, such as is used by chemists, is also to be inserted, as shown 



in rig. 5. The mouth of this may be 

 kept corked when the tube is not in 

 use for watering. 



Water each plant moderately and 

 weigh the plants separately on a 

 balance that is sensitive to one-fifth 

 gram. Record the weights, allow the 

 plants to stand in a sunny, warm 

 room for twenty-four hours, and 

 reweigh. 



Add to each plant just the amount 

 of water which is lost," and continue 

 the experiment in the same manner 

 for several days, so as to ascertain, if 

 possible, the effect upon transpiration 

 of varying amounts of water in the 

 atmosphere. 



Calculate the average loss per 100 

 square inches of leaf surface for each 

 plant throughout the whole course of 

 the experiment. Divide the greater loss by the lesser to find the ratio. Find 

 the ratio of each plant's greatest loss per day to its least loss per day, and 

 by comparing these ratios decide which transpires more regularly. 



Try the effect of supplying very little water to each, so that the hydran- 

 gea will begin to droop, and see whether this changes the relative amount of 

 transpiration for the two plants. Vary the conditions of the experiment for 

 a day or two as regards temperature, and again for a day or two as regards 

 light, and note the effect upon the amount of transpiration. 



The structure of the Ficus (India-rubber plant) leaf has already been 

 studied. That of the hydrangea is looser in texture and more like the leaf 

 of the lily. 



leaves, make blue prints of them, cut these out, and weigh them. The total area 

 may easily be calculated by comparison of the weight obtained with that of a 

 known area of the paper used. 



1 It will be much more convenient to tie the hydrangea, if one has been chosen 

 that has but a single main stem. Instead of the hydrangea the common cineraria, 

 Senecio cruentus, or a small sunflower plant does very well. 



2 The addition of known amounts of water may be made most conveniently by 

 measuring in a cylindrical graduate. 



Fie. 5. A hydrangea potted in 

 battery jar for Exp. XXXVIII 



