39^ APPENDIX. 



into the longer arm until it stands 10 cm. above its level in the 

 short arm. Does the shoot now recover turgor ? Why? Allow 

 it to stand for some days. Does the level of the mercury change ? 



18. To show in what tissues food most readily travels. (U 235.) 

 Girdle as in experiment 16 A a shoot of willow. Cut it off 5 



cm. below ring. Place shoot in water. After some weeks note 

 where new roots are formed. Why? 



19. To show the permeability of stomata for air and their com- 

 munication -with the system of intercellular spaces. (^T*[ 167, 227.) 



Fasten a leaf with a long petiole air-tight in a rubber cork, 

 through which also passes a short glass tube. Fit the cork into 

 a bottle holding sufficient water to cover end of petiole. Attach 

 a filter pump or air pump to glass tube. Observe whether air 

 bubbles leave the end of the leaf stalk. 



Reverse the leaf, so that the blade is immersed, and make same 

 observation. Where do bubbles appear ? Is there any difference 

 between upper and lower sides? 



20. To show the depth to which light may penetrate green tissues. 



a 231.) 



Take a cylindrical pasteboard or metal tube, closed at one end 

 and having a cover which will fit over the closed end. In the 

 end and in the cover cut corresponding holes 1 cm. in diam. Mark 

 side and cover when in place so that holes can be made to coin- 

 cide. On the bottom place a part of a leaf which will cover hole. 

 Slip on cover and observe whether light is transmitted through 

 leaf. Add successive pieces of leaf until no more light passes. 

 What is the color of last light seen ? The examination must be 

 made with direct sunlight, and light completely excluded from the 

 eye except that which passes through the instrument. 



21. Method for detecting considerable quantities of starch in plant 

 organs. (1 233.) 



Boil a few leaves of various plants for a few minutes. Place 

 in alcohol at about 6o° C. until all chlorophyll is dissolved.* 

 Bring the leaves into a tincture of iodine, diluted to a bright 

 brown, for half an hour. The leaves or parts containing starch 

 will become bluish, dark blue, or black, according to amount of 

 starch present. 



22. To show that manufacture of starch occurs only in cells directly 

 illuminated. ("[ 231.) 



* Do not heat over open flame, but set bottle, loosely corked, in a vessel of hot water. 



