TRANSPIRATION 25 



1. Proceed as directed for Experiment 3, using two 

 sound potatoes instead of apples. 



2. The "skin" of an apple is a true epidermis, having 

 an outer layer of cuticle, which is not readily per- 

 meable by water. The "skin" of a potato-tuber 

 consists of several layers of cork cells. It is this 

 corky tissue which chiefly retards the loss or water 

 from the tubers. 



Experiment 5. After noting the color change caused 

 by wetting dry cobalt paper (prepared by dipping 

 filter paper into a solution of cobalt chloride and 

 thoroughly drying it), make the following experi- 

 ment: Place discs of the cobalt paper (e.g., as 

 large as a five cent piece) on opposite sides of a 

 lilac leaf, and hold all in place between two micro- 

 scopic slides (or larger pieces of glass), fastened 

 with rubber bands around each end. Compare the 

 rate of color change of the two opposite discs, and 

 infer the cause. 



Other leaves, having structural peculiarities 

 similar to those of the lilac, may be used; e.g., 

 hibiscus, osage orange, oleander, lizard's tail 

 (Saururus) . 



Experiment 6. Examine, with the microscope, strips 

 of both upper and lower epidermis of the leaf used 

 in Experiment 5, and infer the probable cause of 

 the differential color-change observed. 



Experiment 7. Place any suitable, well- watered potted 

 plant on postal scales, "household" scales, or other 

 convenient weighing device, after first carefully 

 wrapping the pot in sheet-rubber, or sheet-oil- 

 cloth, as in Experiment i . Record the loss of weight 

 at fifteen-minute (or other suitable) intervals while 

 the experiment is standing for an hour, each, in (a) 



