SELAGINELLA 149 



scope, using low and high powers, and describe 

 all details of leaf-structure thus brought out, 

 including 



(b) The shape and arrangement of the cells; the 

 color, size, and distribution of the plastids in 

 the cells; any other cell contents; 



(c) Variations between marginal cells, those along 

 the central axis, and those lying between. 

 Account for any constant differences observed. 

 Do you think any observed differences may be 

 attributed to environment? Explain. 



(d) Can you identify a tiny, membranous flap, 

 the ligule, near the leaf -base? On which side 

 of the leaf (dorsal or ventral) is it? Be sure 

 to examine both sides of the leaf in this connection. 



(e) Are there stomata? If so, describe their 

 location. 



(/") Make drawings sufficiently large to illustrate 



all points observed under D. 

 2. The Stem. 



(a) With the razor, make thin cross-sections of 

 the stem, and mount them in water or clearing 

 fluid. 



(b) Is the stem differentiated into (i) epidermis; 

 (2) vascular regions; (3) fundamental tissue 

 (cortex)? If so, describe. 



(c) Note the presence or absence of air-spaces. 



(d) Compare the tissue-system of the Selaginella 

 ( stem with those in the fern. 



(e) Describe the distribution of xylem and phloem 

 in the vascular bundle. 



(/) Do you find indications of vascular bundles 

 passing out to the leaves? 



