STUBIES OF TJIK LEAF 



G7 



the weight, leave l.lie plant couiiteilialanced on tlie scales. In a 

 relatively short time it will be seen whether tlie plant gains or 

 loses. 



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

 again some liours later the same da}' ; if not, the next day. Kecord 

 weight and time. 



Let tlie plant now remain in darkness as nearly as [lossible an eqnal 

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



AVhat has caused the change; of weight? (Befoie the answer is re- 

 quired, tlie 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 tilled 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 through 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, ilue to the activity 

 of the leaf under the influence of light and lieat, 

 should be seen. 



Experiment 15. — Relative activity of the 

 upper and under sides of the Begonia leaf. — a^. 

 Two dry watch glasses are to be placed on oppo- 

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

 and held in place liy a cliji, or bj' two wooden 

 strips and elastic bands, as in the figure. Two 

 inclosed spaces are thus made, on the ruider 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? 54 



Experiment 16. — Secure two mature leaves 

 of the India Uubber Plant (Ficux eUixtica). 

 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 eacii 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 10 may be given to different pupils, or groups, 

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

 for a whole class or divisioQ. 



Method of liolding 

 watch glasses 

 (tc) upon Begonia 

 leaf. 



