A YEAR IN SCIENCE 89 



once to the pith? In a cross section of the stem, locate 

 the parts seen in the longitudinal section. Note the 

 lines running through the wood from the pith to the 

 hark. These lines of pith are called medullary rays. 

 How does the arrangement of the wood in the box 

 elder stem differ from that in the corn stem? Make 

 a drawing of both the longitudinal and cross section 

 of the box elder, and label the parts. These stems are 

 examples each of the two classes of stems of flowering 

 plants. The corn stalk is an example of the monocoty- 

 ledenous type, and the box elder of the dicotyledenous 

 type. 



Exercise 60. Functions of Stems. 



Object : To determine one of the functions of stems. 



Apparatus 



Impatiens stem Beaker 



Eosin solution Scalpel 



Potato 



Directions: Cut off a number of branches of the 

 Impatiens, of the Coleus, or of any other plant with a 

 thin epidermis, and immediately place the cut end in a 

 beaker of eosin solution. Similarly, cut off the end of 

 a potato and place the cut end in the eosin solution. 

 Set them aside for several hours. Then examine the 

 stems to determine the paths taken by the red solu- 

 tion. To see this more clearly, make a longitudinal 

 section of the stem. What part of the stem is stained, 

 the pith, wood, or epidermis? Does this stain extend 

 into the leaves ? What is its course through the leaves ? 



