THE PLANT GROUPS 117 



(2) Root traces. The root bundles which enter the 



lateral roots may sometimes be found leaving 

 the vascular cylinder. Do they leave a gap as in 

 the leaf bundle ? 



(3) Drawing. Outline your entire section, indicating 



the main tissue layers and their subdivisions and 

 the relations of leaf trace, leaf gap, and cen- 

 tral cylinder. How does Adiantum differ from 

 an herbaceous plant like Salvia in its gross 

 anatomy ? Consult the text discussion of Salvia 

 in Part I. 

 e. Minute structure of the tissues. 



(1) Epidermis, cortex, and pith. Draw in detail a few 



characteristic cells of each of the above layers 

 and their main subdivisions, to show the dis- 

 tinctive cell characteristics of each tissue. Label 

 the parts of the cells. What is the function of 

 eacli cell type in the rhizome, and how is its 

 structure adapted to its function ? 



(2) Vascular cylinder. Study the following tissues of 



the vascular ring and leaf trace critically with 

 low power : 



() Xylem. Characterized by large water-carrying 

 cells resembling ducts in higher plants. 

 These xylem cells, or tracheids, stain red 

 where sections are stained with safranin 

 (the dye commonly used in staining xylem). 

 Are there rays or other living tissues in the 

 xylem of ferns, as in that of higher seed 

 plants previously studied ? 



(7>) Pldoe'm. Surrounding the xylem. The sieve 

 tubes are the large cells seen in the phloem 

 flanking the xylem on either side. 



