394 APPENDIX. 



9. To show that water is not absorbed by leaves in quantity ade- 

 quate to supply evaporation. (^[ 196.) 



Cut off a vigorous shoot of a plant with abundant foliage ; 

 close end of stem with grafting wax ; expose to sunlight until 

 slightly wilted ; then immerse it in water. Does the plant recover 

 its turgidity ? 



10. To show that many leaves are not wetted by -water. (*[ 210.) 

 Immerse various sorts of leaves in water. Does the water wet 



the surface? What is the cause of the silvery reflection of light 

 from the surfaces of some ? What relation does this repulsion of 

 water have to blocking of stomata by rain? 



11. To show the loss of -water by evaporation. (If 208.) 



Clean and dry the surface of a pot in which a thrifty single- 

 stemmed plant is growing ; close the hole in the bottom with a 

 cork ; with a brush paint the whole surface with a thick layer of 

 melted paraffin. Cut out'a piece of stiff paper which will fit 

 around stem and just cover the soil in pot. Using this as a pat- 

 tern cut a cover for the soil from a sheet of lead ; slit the cover 

 from the central hole to circumference ; adjust it around plant 

 and cement all cracks with grafting wax.* Weigh. Weigh again 

 at intervals of 24 hours, for 4 days. 



12. To show the variation in the rate of evaporation due to the 

 difference in structure of the organ. (^\^\ 209, 438.) 



Compare as shown by shrinkage or by loss of weight, (a) 

 Through cork tissue and without it. Take two potatoes ; peel 

 one ; expose side by side ; compare day by day. (b) Through skin. 

 Compare in same way two apples, (c) Through stomata. Take 

 three equal leaves of oleander; of one close the stomata (which 

 are on under side only) with a thin coat of grafting wax, or cocoa- 

 butter melted and brushed on (taking care not to kill cells by 

 having wax too hot) ; coat the upper surface of second in same 

 way ; leave third uncovered. Compare day by day. 



13. To show the conditions affecting evaporation. (^T 210.) 

 Construct a potometer as follows : Bend the central stem of a 



T-tube until it is parallel with the cross piece. Fit into the lower 

 opening of the straight leg a capillary tube 30-40 cm. long, with 

 3 cm. of each end bent at right angles to the main part and in 

 opposite directions. Into the bent leg fit a shoot of a thrifty 

 plant cut off under water, at the same time filling the j-t"be with 



*Or the pot can be set in a tin vessel which it fits and the lead cover luted to this. 



