THE STEM. 39 



3. Examine the wood closely. Notice the medullary 



rays, appearing like lines radiating from the pith. 

 Careful inspection shows numerous openings in 

 the wood between the medullary rays. These are 

 the ends of vessels that convey water and air 

 through the stem. It can also be observed that 

 the pith is made up of minute cells. These struct- 

 ures may be seen still more readily in the grape- 

 vine. 



4. With the stem of the apple-tree compare those of the 



grape-vine, common elder, and oak, making trans- 

 verse sections, as before. In what respects do 

 they all agree ? How do they differ? 



II. Examine the stem of Indian corn, making both 

 transverse and longitudinal sections. What part of the 

 stem has the firmest tissue ? 



Make an outline sketch of the transverse section, show- 

 ing the position of the woody parts as they appear under 

 a good lens. Compare with this a similar section of the 

 stem of a palm or other monocotyledonous plant. Com- 

 mon greenbrier is suitable for this purpose. 



III. Study shoots of white pine, two or three years old, 

 that have lain some time in alcohol. Indicate by means 

 of a diagram the relative position of pith, wood, and bark. 



Using $n older, dry specimen, that has been cut so as 

 to show a smooth transverse section, notice the succession 

 of annual rings. How does the outer edge of each ring 

 differ from the inner? Determine the age by counting 

 the number of rings. Examine the stem of the arbor 

 vitae or red cedar, and see if it corresponds in structure 

 with that of the white pine. 



IV. Write an account of the different stems you have 



