88 LABOKATORY MANUAL 



How would you determine the age of the branch from 

 the external markings? From the external structure, 

 how would you distinguish a stem from a root ? Draw 

 a twig to show the above mentioned parts. 



Exercise 59. Internal Structure of Stems. 

 Object: To study the internal structure of stems. 



Apparatus 



Box elder twigs Scalpel 



Corn stems Dissecting microscope 



Directions : A. Corn Stem : Take an internode of an 

 old corn stalk. Note on the cut end the outer rind 

 surrounding the pith. Throughout the pith note the 

 small dots of woody substance. Break the stalk into 

 two parts. What do you find the small dots to be? 

 Cut a longitudinal section and follow a few of the 

 small fibres. Do they pass the length of the internode ? 

 Through the node into the next internode? These 

 thread-like fibres are called fibro-vascular bundles. 

 Make a drawing showing these points. Under the lens 

 of the dissecting microscope examine a cross section 

 of the corn stem. Are the bundles regularly arranged ? 

 Where are they most numerous, near the margin or 

 toward the center? Can you determine of what the 

 rind is composed? Make a drawing to show these 

 points. 



B. Box Elder Stem : Make a longitudinal section of a 

 small piece of box elder stem. How many parts do you 

 distinguish? Where is the wood in this stem in refer- 



