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). 
(6) The central bud. 
(c) The bulb-scales. 
(d) 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. — Grape sugar is an impor- 
tant substance among those stored for food by the plant. 
It received its name 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 by boiling with diluted sulphuric acid. 
In the plant it is made from starch by processes as yet 
imperfectly understood, and another sugar, called maltose, 
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. 
Channels for upward movement | in dicotyledonous stems several 
of water . 2... es years old. 
[in monocotyledonous stems. 
Channels for downward move- [{ in dicotyledonous stems. 
ment of water . . . . ~- lin monocotyledonous stems. 
Channels for transverse move- 
ments. 
kinds stored. ~ 
uses. 
where stored. 
Storage of plant-food . . | 
