LEAVES 



159 



No. 3. Coat lower surface with vaseline. 



No. 4. Coat both surfaces with vaseline. 



Also vaseline the leafstalk of each leaf. After a few hours 

 make observations on all the leaves. Re- 

 sult ? 



Conclusion. Which surface gives off most 

 water ? 



141. LEAVES 

 Object. Same as in Experiment 140. 



Apparatus. Two watch glasses, any plant 

 with large succulent leaves, and a rubber band or 

 other means of fastening the glasses in place. 



Method. Place the watch glasses on 

 opposite sides of the leaf and allow them 

 to remain there in a shady place for some 

 time. 



In which glass does most of the dew 

 collect? 



Conclusion. Same as in Experiment 140. FIG. 69. 



142. LEAVES 



Object. Same as in Experiment 140. 

 Apparatus. Cobalt paper, 1 leaves, and plates of glass. 



Method. Dry the cobalt paper over the flame of a lamp. 

 Lay a dry leaf between two pieces of the dried cobalt paper. 

 Place the whole between plates of glass which have been 

 wiped perfectly dry. 



1 Cobalt paper is prepared by wetting filter paper with a solution 

 of cobalt chloride. Dry it thoroughly over a gas flame until it be- 

 comes blue. Dampness in air will cause the blue to disappear and 

 the paper will become red. 



