STUDIES OF THE LEAF 



67 



the weight, leave the plant counterbalanced on the scales. In a 

 relatively short tinae it will be seen whether the plant gains or 

 loses. 



Set the plant in a sunny or well-lighted place. If possible weigh 

 again some hours later the same day ; if not, the next day. Record 

 weight and time. 



Let the plant now remain in darkness as nearly as possible an equal 

 length of time. Again weigh, and record weight and time. 



What has caused the change of weight ? (Before the answer is re- 

 quired, the next experiment will naturally have been done ; there will 

 be additional reason to assign the change of weight to one particular 

 cause.) What effect has light upon the rate of change? 



Experiment 14.^ — Two tumblers, a piece of pasteboard, a piece of 

 sheet rubber large enough to cover the mouth of the tumbler, and a 

 leaf, are needed. One tumbler is nearly filled with water. The paste- 

 board, with a hole in it, is placed on this tumbler. A puncture is 

 made in the middle of the rubber, the rubber stretched, and the leaf- 

 stalk put througli the puncture. The leaf is now put on the tumbler, 

 its stalk descends into the water through the hole in the pasteboard. 

 The blade of the leaf is now covered with the second tumbler, and the 

 apparatus set in the sun. 



In a few minutes an effect, due to the activity 

 of the leaf under the influence of light and heat, 

 should be seen. 



Experiment 15. — Relative activity of the 

 upper and under sides of the Begonia leaf. — 

 Two dry watch glasses are to be placed on oppo- 

 site sides of a Begonia leaf (still on the plant) 

 and held in place by a clip, or by two wooden 

 strips and elastic bands, as in the figure. Two 

 inclosed spaces are thus made, on the under and 

 upper faces of the leaf respectively. Neither 

 should be in direct sunlight. Examine the 

 watch glasses for a deposition of moisture after 

 fifteen or twenty minutes, or longer. Which side 

 of the leaf exhales moisture the more rapidly? 



Experiment 16. — Secure two mature leaves 

 of the India Rubber Plant (Ficus elastica). 

 After smearing the under face of one and the 

 upper face of the other with vaseline, as well as the cut end of the leaf 

 stalk in each case, so as to prevent the escape of moisture from these 

 surfaces, hang the two leaves side by side to dry. When either one is 



1 Experiments 14, 15, and 16 may be given to different pupils, or groups, 

 simultaneously, as one or two preparations of each experiment will serve 

 for a whole class or division. 



a>!f=-.-: 



54. 



Method of holding 

 watch glasses 

 {to) upon Begonia 

 leaf. 



