136 LABORATORY AKD FIELD EXERCISES 

 ANATOMY OF THE SPRUCE STEM 



TRANSVERSE SECTIONS 



Cut thin transverse sections from living spruce twigs about 

 one eighth of an inch in diameter. Mount some sections in 

 alcohol and some in iodine solution. Observe the latter sections 

 for starch storage, wood rays, pith, etc. 



1. The main tissue layers of the spruce. 



a. Compare the tissue layers of the spruce with those of 



the lilac and fern. Which stem does the spruce most 

 nearly resemble in structure ? Does the spruce pos- 

 sess both a cork cambium and the cambium which 

 forms phloem and xylem ? Note carefully the rela- 

 tions of corky bark, green cortex, phloem, cambium, 

 xylem, and pith. 



b. Leaf gaps and traces. Observe the shape of the pith. 



Do you find lobes of the pith (leaf gaps) extending 

 into the xylem ? If so, note their extent and the 

 nature of the xylem ring opposite them. Leaf traces, 

 looking like wide wood rays, often appear opposite 

 these pith lobes or leaf gaps in the spruce. Consult 

 the text figures. 



c. Observe sections stained with iodine for starch-storage 



areas. Where is starch stored in the spruce ? 



d. Make an accurate drawing of your section in outline 



(no cells), indicating the main tissue areas and their 

 limits. Include wood rays, annual rings, leaf gaps, 

 and leaf traces. Study the text and label your 

 drawing accurately. 



e. Summary. Write an accurate and concise summary of 



the structure of the spruce stem in the form indicated 

 for herbaceous dicotyledons and for the fern. Indicate 



