EXERCISE 31 



WHAT PROVISIONS ARE MADE ANNUALLY FOR NEXT 

 YEAR'S GROWTH OF BRANCHES? FOOD STORAGE 



Materials. Twigs of any common tree or shrub which has large 

 buds, buckeye, horse-chestnut, and some hickories are best; lilac is 

 common everywhere and is satisfactory ; iodine solution ; Millon's 

 reagent. 



Directions for work. Split a twig and bud lengthwise. Apply 

 iodine to the freshly cut surface of one half. Is there any evi- 

 dence of the presence of food in the form of starch ? Is the 

 quantity relatively great ? Microscopic examination of thin cross 

 sections of the stem stained with iodine may aid in estimating 

 the amount of starch present. Is starch principally in the bud 

 or in the stem ? 



In like manner apply Millon's reagent to the cut surface of 

 the other half of the twig and bud. This reagent produces a 

 red color, after five or ten minutes, if protein is present. How- 

 ever, since the living substance in all cells (protoplasm) is a 

 protein, the red color may not be taken to indicate stored 

 protein food unless the color is pronounced. 



What are the facts as you find them regarding the reserve 

 supply of these two classes of foods in the stem and the bud ? 



Does it appear to you that the amount of reserve food would 

 be sufficient to maintain the spring growth from the buds for 

 a long time, or will the new growth apparently soon depend 

 upon the manufacture of food by the new leaves? As you 

 recall your observations of the opening of buds and the begin- 

 ning of growth in spring, are the new leaves actually exposed 

 to the light early or late during the spring growth? 



Sum up in your notes all your observations of facts which 

 would influence the new growth in the spring. 



References 



BERGEN and CALDWELL. Practical Botany, pp. 77, 78. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 43, 44. 



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