CHAPTER VI 



FOOD RESERVOIRS 



75. Storehouses. — All greatly thickened or congested 

 parts are reservoirs for the storage of plant-food. This 

 food is mostly starch or sugar. Potatoes, beets, turnips, 

 thick rhizomes, seeds, are examples. Recall how potatoes 

 sprout in the cellar (Fig. 45) : the sprouts are produced from 

 the stored food. 



76. The presence of starch can be determined by apply- 

 ing diluted tincture of iodin to the part: if a blue or purplish 

 brown color appears, starch is present. Cut the part open and 

 moisten the fresh sur- 

 face with iodin (to be 

 had at the drug store) . 

 The test will usually 

 give the best reaction 

 when the part is per- 

 fectly dormant. Starch 

 may be found in 

 nearly all twigs in fall 

 and winter. Test thin 

 cross-sections. 



77. This stored 

 plant-food enables the 

 plant to start quickly 

 in the spring, without 

 waiting for food elab- 

 oration to begin in the 

 leaves; and it enables 

 the plantlet in the 



Potato sprouts. The sprouts have Used the food 

 Btored in the tuber, and the tuber has shriveled. 



(31) 



