174 TRANSPORT OF FOODS 



tangential sections of leaves free-hand coat thinly one end of 

 a cork with melted rosin 2 parts and vaseline i part, and while 

 this coating is yet warm press into it a piece of leaf that has 

 lain for a while in 95 per cent, alcohol, first allowing the alco- 

 hol to evaporate from its surface. With a little practice sev- 

 eral good sections can now be cut from surface to surface. If 

 preferred the sections may be cut on a sliding microtome. 



3. Cut some of the veins in leaves about sundown and darken 

 them so that they cannot photosynthesize before they are ex- 

 amined the next morning, when they are to be bleached in hot 

 alcohol and placed in an iodine solution. Does this reveal any- 

 thing about the food-conducting function of the veins? An 

 outline drawing colored lightly with a blue pencil where starch 

 occurs will make a good record of this observation. 



4. Girdle stems in the spring and note thereafter growth in 

 diameter above and below the girdle. Study sections to note 

 storage of food in both regions. 



