394 APPENDIX. 



g. 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, (^f 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. (^[ 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 shozu the conditions affecting evaporation, (^f 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 T-tube with 



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



