194 PRACTICAL BOTANY. 



5. Centrally lies the Xylem, in which also two con- 

 stituents may be recognised 



a. Tracheides, which appear polygonal in transverse 

 section, and have large cavities, with no cell-contents : 

 the walls are thick and lignified, and show a peculiar 

 structure which will be explained by a comparison with 

 what is seen in longitudinal sections. 



6. Parenchymatous cells, with cellulose walls, and 

 protoplasmic contents and starch. These cells are 

 distributed evenly throughout the xylem, and also form 

 a band surrounding it completely. 



N.B. The parenchyma in both phloem and xylem 

 being fundamentally of similar nature may be united 

 under the general term Conjunctive parenchyma. 



Cut similar transverse sections of the stem of Pteris or 

 Davallia, and note that the outlines and arrangement of the 

 tissues are more regular than is the case in Aspidium. 



VIII. Cut longitudinal sections of the stem of the 

 Male Fern. First take radial sections of the peripheral 

 tissues, and treat as above : note 



1. The Epidermis, with scaly hairs. 



2. The sub-jacent ground tissue, and especially the 

 Sclerenchyma, consisting of cells of short, prosen- 

 chymatous form, with brown pitted walls, and cell- 

 contents : note the gradual transition from the scleren- 

 chyma to 



3. The colourless ground-tissue, with short paren- 

 chymatous cells, and large intercellular spaces. 



IX. Then cut longitudinal sections, so as to pass 

 tangentially through the central network of bundles : 

 treat some sections with Schulze's solution, and mount 



