42 LABORATORY AND FIELD EXERCISES 



of these scars and markings and what caused them ? 

 Observe the bark carefully with a hand lens ; do 

 you tind any minute markings ? Have they a definite 

 form and distribution ? 



b. Drawings. Draw a portion of the shoot you are exam- 

 ining, representing three years of growth in length. 

 Indicate clearly the appearance and position of the 

 buds, the scars marking annual growth in length, 

 leaf scars, leaf-bundle scars, and lenticels. For the 

 meaning of these terms consult the text. 



GROSS STRUCTURE OF MATURE STEMS 



Study wood blocks (preferably oak) cut in cross and in long 

 section from branches of trees. To give the best results these 

 blocks should be smooth and polished. Observe with naked 

 eye and hand lens. Consult the text for a general discussion 

 of the structures observed below. 



TRANSVERSE SECTIONS 



1. Bark. Compare the bark of a mature branch in sectional 



view and on its surface with that of the twigs observed 

 above. Is the epidermis still present ? the green bark ? 

 Compare the bark of a branch of the elm with that of 

 some other tree in wood blocks. What kinds of tissue 

 are most prominent in the bark on the branches and 

 trunks of trees ? 



2. The cambium. Locate the position of the cambium layer, 



represented by a line just outside of the wood. 



3. The wood cylinder. 



a. How many annual growth rings are represented in the 

 block you are examining ? How is the boundary line 

 between the summer and spring wood of successive 



