22 



THE VEGETATIVE ORGANS 



Sweet-Pea with those of the Bean. What are the most 

 important points of agreement or difference ? 



Food stored in the cotyledons. Seeds like the Garden Pea 

 and the Bean are common articles of food. In what 

 does the nutriment consist, and where is it contained ? 

 An instructive, though only partial, answer is easy to find. 



Place a little powdered laundry starch in a test tube, 

 add water, and boil for a few minutes. Allow it to cool, 

 add a drop of iodine solution, 1 and note the dark violet 



Fig. 8. Fruit of Sunflower. i, side view ; 2, fruit opened 

 and one cotyledon removed ; c, cotyledon ; fu, funicle ; pe, peri- 

 carp ; pi, plumule ; ra, radicle ; sc, scar ; /, testa. 



colour produced. Repeat the experiment with flour, and 

 a slice of potato ; the same violet coloration is seen. 

 This coloration indicates the presence of starch ; in other 

 words, the addition of a solution of iodine to a starch- 

 containing substance produces a violet coloration. Now 

 take a cotyledon of the Bean and place a drop of iodine 

 solution on its uninjured surface. Scratch the surface of 

 another cotyledon, add iodine solution to the scratched 



1 A solution of iodine and potassium iodide in water. 



