LABORATORY AND FIELD EXERCISES 



cork layer? How many tissue layers of different 

 appearance are there between the outer cork layer 

 and the outer limits of the wood ? Observe the cells 

 of these different layers with a low power and note 

 the general character of each. Consult the text and 



-PUh 



FIG. 13. Healing of a wound due to the severance of a branch 



The healing is done hy new tissue, called callus, formed over the wound. Ohservo 



the irregularity of the annual rings around the wound. Redrawn from Curtis's 



" Nature and Development of Plants " 



Fig. 46 for a discussion of these tissue layers belong- 

 ing to the bark. See also Fig. 52 of the text. 

 b. The wood. Note the following main tissues and struc- 

 tures of the wood : 



(1) Note the number and relative cell width of the annual 

 rings of growth; the distinction between spring 

 and fall wood ; the wood rays. The relative length 

 and termination of the wood rays can now be 

 accurately traced. Do they extend through the 

 phloem ? 



