and Laboratory Methods. 



2047 



hyacinth {Hyacinthiis). Divide this column into at least five longitudinal sec- 

 tions each of which shall have a strip of epidermis on one side. Lay each strip 

 of tissue on a piece of paper and with a soft lead-pencil quickly draw a line to 

 indicate the length and curvature of each strip, then place a strip in each of five 

 potassium nitrate solutions, .5 percent., 1 per cent., 1.5 percent., 2 percent., 2.5 

 per cent. After 10-20 minutes remove the strips from the solutions, lay each 

 one beside the line corresponding to it and draw another line to indicate the 

 change in curvature. The strip which has lain in the solution which is just iso- 

 tonic will show no change in curvature, those in solutions weaker than the cell 

 sap will show greater curves, those in solutions stronger than the cell sap will 

 straighten as a result of plasmolysis. 



3. Tissue=tension. Cut a leaf-stalk of Richardia 20 cm. or more in length 

 and measure its length precisely. With a sharp scalpel cut a superficial longi- 

 tudinal slice about 2 mm. in thickness the whole length of the stalk. After a 

 few minutes it will be found to be several millimeters short of its original length. 

 Next remove the entire epidermis from the central column of pith and determine 

 its increase in length. 



The transverse tangential tension may be illustrated by taking a transverse 

 disk 3-4 mm. in thickness and separating, by means of a sharp scalpel, a ring 

 of outer tissue 2 mm. in thickness from the inner tissue. While the outer ring 

 still encloses the center, cut through the former and place them both in water. 

 After 15 minutes the outer ring is no longer sufficient to enclose the center. 



VII. TRANSPIRATION. 



1. Lifting Power of Evaporation. Tie a piece of animal membrane over the 

 bowl of a thistle-tube while the tube is wholly immersed in water ; without allow- 

 ing any air to enter, support the tube in an upright position with the small end 

 standing in a dish of mercury. The mercury 

 will rise in the tube until its weight draws in air 

 through the membrane. 



2. Lifting Power of Transpiration. Fill a 

 U-tube with water, support it in an upright posi- 

 tion, and in one end fasten a stem of some 

 plant, using a rubber stopper and allowing the 

 cut end of the stem to project a centimeter 

 beneath the stopper. The stem should be cut ofif 

 under water and kept in water until placed in the 

 final position in order to keep the cells cut 

 across from filling with air. Into the open end 

 of the U-tube pour mercury until it stands 3 or 

 4 cm. higher in the open arm of the tube than in 

 the closed arm. The weight of the mercury 

 column will inject the stem with water. Allow 

 the preparation to stand until the stem wilts, 

 noting the rise of mercury in the closed arm at 

 regular intervals. 



Fig. 



A Potometer. 



The horizontal glass tube is 

 60-75 cm. in length. (Not 

 shown in the figure. ) 



