66 COMMON LIVERWORT. 



MINUTE ANATOMY. 



A. THE TRICHOMES. Remove some of the hairs 

 that are pressed tightly upon the under surface of the 

 wings of the stem, and under high power notice 



1. The shape. 



2. The internal projections i sometimes horn-like, branched, 

 and extending quite across the cavity of the hair. 



3. The more or less prominent spiral constriction on which 

 the projections are seated, giving the walls in optical 

 section the appearance of alternate scallops. 



4. Draw. 



5. Compare the loose silky hairs along the middle of the 

 stem, the true rhizoids, with the preceding. Draw. 



Mount marginal and intermediate scales, and notice 



6. The cellular structure of each. Draw. 



B. THE STEM OR THALLUS. Remove a thin slice 

 from the upper surface of the stem, mount with the free 

 surface uppermost, and under high power notice 



1. The surface or epidermal cells; their shape and con- 

 tents. 



2. The large breathing pores or stomata, encircled by 

 rows of special cells, the supplementary guard-cells ; 

 number of cells in each circle. 



3. Draw a stoma with some surrounding tissue. 

 Remove the cover-glass, remount the section with the 



free surface downward, and disregarding other features, 

 notice 



4. The four innermost (now lying uppermost) cells of the 

 stomata, having more or less prominent projections 

 (sometimes obsolete) arching over toward the center 

 of the pore, the true or active guard-cells. Draw. 



