HOW THE PLANT USES THE FOOD IT MAKES 83 



What is the effect of girdling? Willow twigs as thick 

 as a lead pencil and about eight inches long may be 

 girdled half an inch above the lower end and placed in 

 water so that the cut surfaces are covered by the water. 

 Some of the twigs should not be girdled, but placed 

 in water for comparison. Make deep and shallow 

 girdles, some clear around and some only part way. 

 In girdling, cut away the bark and bast clear to the wood. 



If the food cannot pass the girdle the roots will come 

 out just above it. But if it passes beyond it the roots 

 will come out at the very bottom, as they do in the 

 twigs which are not girdled. 



Just outside the bast is the green rind; this is where 

 most of the starch and sugar pass down from the leaves 

 on the way to the roots and other places where they 

 are needed. 



The kinds of food. In seeds we find (1) starch, 

 (2) fats and oils, (3) protein. All these may be easily 

 known by simple tests. 



What foods are found in the seeds familiar to you ? 

 You may test for starch by putting iodine solution 

 (see page 74) on the broken or cut surfaces of well- 

 soaked seeds. 



You may test for fats and oils by scraping the seed 

 with a knife, so as to make a fine powder. Put this on 

 white paper ; place the paper on a piece of tin and heat 

 it (taking care not to let it scorch). The fat or oil will 

 make a spot on the paper. 



