A TRICHUM UND ULA TUM. 9 l 



b. The axial, with the cell walls colorless. 



c. The intermediate, with cell walls yellowish. 



2. '\\it peripheral tissue. Note 



a. The outer layer, epidermis, occasionally bearing 



root-hairs. 

 l>. The similar underlying cells, merging into 



3. The intermediate region. Note 



a. The larger cells with the walls becoming thinner 



toward the center of the stem. 



b. One or more leaf traces, composed of 



i. A crescent shaped layer of small round cells 

 with very thick walls, the dorsal cells. 



ii. Lying in the crescent, about two rows of 

 larger cells with rather thin walls, the conduct- 

 ing cells, inclosing 



iii. Two or three small cells, appearing much 

 like intercellular spaces, the central cells. 



iv. Still further toward the center of the stem, a 

 few scattered cells similar to the dorsal, the 

 basal cells. 



c. Note that the leaf traces nearest the center of the 

 stem are the simplest. Sometimes one may be found 

 at the very center of the stem. 



4. Draw one of the largest leaf traces with some of the 

 surrounding tissue including the adjacent epidermis. 



5. Theaxia/ region. Note 



a. The more or less strongly thickened walls of the 

 cells. 



b. The small groups of cells with the intervening walls 

 very thin and membranous. 



c. Draw a portion of the axial region. 



6. In a longitudinal section of the stem, identify as many 

 of the different sorts of cells as possible, noticing 



