216 PRACTICAL BOTANY. 



These resin ducts are connected with the cortical resin 

 ducts by channels through the medullary rays. 



Using a piece of fresh green stem, cut thin cross sec- 

 tions and examine them for cell contents. Where is 

 chlorophyl found ? Determine in what parts of the sec- 

 tion starch is present; examine particularly the cells of 

 the cortical parenchyma, those surrounding the resin ducts, 

 and the phloem. Try to find crystals in the cells in the 

 phloem region. Look for resin ; it may be tested for by 

 tincture of alkanna. If the section is taken in the rapidly 

 growing season, examine the cells of the cambium layer 

 for cell contents and nuclei. State in what condition you 

 find the cells of the xylem. 



9. Cut thin radial sections of the stem. Do not try to 

 get large sections ; a narrow slice from the epidermis to 

 the pith will show every point of the structure. Mount 

 in Schultze's solution. Draw and locate all the parts 

 pointed out in Fig. 135. 



Under the high power study the cambium layer, start- 

 ing with the narrowest cells and examining all in succes- 

 sion out towards the phloem. What is the shape of the 

 cells? Are the end partitions easily seen? Is the proto- 

 plasm abundant or scanty ? Do you find a nucleus ? 



Describe the cells of the phloem. Find long cells with 

 irregularly circular patches of sieve plates on their sides ; 

 these are sieve tubes. Draw. Can you find crystals in 

 any of the cells of the phloem ? 



Examine the cells of the cortical parenchyma. What 

 is their shape as seen in the radial section? Find resin 

 ducts. It may be necessary to examine several sections, 

 as all may not have passed through a resin duct. Draw 

 some of the glandular cells with a few of the adjacent 

 cells of the cortical parenchyma. Draw also a few of the 

 cells of the cork layer and epidermis. Starting again with 

 the narrowest cells of the cambium, compare the transition 



