WORK OF THE STEM 85 



Split another onion from top to bottom and try to find : 

 (a) The plate or broad flattened stem inside at the base (Fig. 34). 

 (J) The central bud. 

 (c) The bulb-scales. 



{(1) In some onions (particularly large, irregular ones) the bulblets 

 or side buds arising in the axes of the scales near the base. 

 Test the cut surface for starch. 



101. Plant-Foods in the Onion. — G-rape sugar is an impor- 

 tant substance among those stored for food by the plant. 

 It received its namd from the fact that it was formerly 

 obtained for chemical examination from grapes. Old, dry 

 raisins usually show little masses of whitish material 

 scattered over the skin -which are nearly pure grape sugar. 

 Commercially it is now manufactured on an enormous 

 scale from starch Ijy boiling with diluted hydrorliloric acid. 

 In the plant it is made from starch by processes as yet 

 imperfectly understood, and another sugar, called. ?waZiose, 

 is made from starch in the seed during germination. 



It may be readily shown by suitable experiments that 

 the onion contains both grape sugar and proteids. 



102. Tabular Review of Experiments. — [Continue the table from 

 Sect. 38.] 



103. Review Summary of Work of Stem. 



'in young dicotyledonous stems, 

 in dicotyledonous stems several 



years old. 

 in monocotyledonous stems. 

 Channels for downward move- ( in dicotyledonous stems. 



ment of water l_ in monocotyledonous stems. 



Channels for transverse move- 

 ments. 



'where stored. 

 Storage of plant>-food . . . . J. kinds stored. 



Channels for upward movement 

 of water 



