THE PLANT GROUPS 137 



in the summary the particulars in which the spruce 

 stem resembles that of the fern, and the significance 

 of this resemblance. Consult the text on the structure 

 of the spruce stem. 



2. Structure of the tissues (prepared slides). Observe with 

 low and high powers of the microscope the tissue layers 

 and tissue elements in stained preparations of spruce 

 stems. 



a. The cork lark. Of what kinds of tissue is it composed ? 



Is there an apparent tendency to form separating 

 scales ? Are the cells of the cork bark living or 

 lifeless ? The cork cambium forms an inner layer of 

 rectangular living cells on the inner side of the cork 

 layers in the spruce. 



b. Cortex. Observe the character of its cells and the struc- 



ture of the large resin canals with a lining layer of 

 small resin secreting cells. 



c. Phloem and cambium. Can you differentiate the phloem 



and cambium layers ? Does the phloem show annual 

 growth layers corresponding to those of the xylem ? 

 What marks the outer boundary of each annual layer 

 of phloem (this outer limit of the phloem can be 

 determined by the outer limit of the wood rays) ? 



d. Xylem. 



(1) Annual rings, composed of spring and summer wood. 

 Compare these with similar structures of woody 

 dicotyledons. How do the tissue elements of the 

 spring and summer wood differ in the spruce 

 from similar structures in lilac and alder ? Which 

 kind of wood is better adapted for rapid water 

 conduction ? Is the wood structure adapted to 

 the leaf structure and transpiration requirements 

 in the spruce ? 



