- 28 - PINUS. 



56. Structure of Stern. Draw a segment of the stem of a young pine tree, showing : 

 bark ; cork ; resin canals ; phloem ; cambium ; wood ; annual rings, with spring and 

 autumn wood ; medullary rays ; pith. Estimate the age of the stem. 



57. Histology of Stem. Draw under the low power a transverse section of a young 

 stem, showing : epidermis ; scale-leaf bases ; cortex ; resin-canals ; phloem ; cambium ; 

 xylem ; medullary rays ; pith. Then draw a sector under the high power showing, in 

 addition: sieve-tul.es and phloem parenchyma; bordered pits on radial walls of tra- 

 cheides ; secretory cells of resin-canals. 



