XV.] THE BRACKEN FERN. 453 



3. Cut a thin transverse section of the rhizome, mount 

 in water and examine with 1 inch obj. 



a. The single layer of much thickened epidermal 

 cells. 



b. The small opaque angular contours of the 

 hypodermal cells (external sclerenchyma). 



c. The large polyhedral more transparent paren- 

 chymatous cells. 



d. The small opaque angular contours of the cells 

 of the internal sclerenchyma. 



e. The great openings of the vessels in the fibro- 

 vascular bundles. 



Draw the section. 



4. Examine with \ obj. 



a. The epidermis: its thick-walled cells. 



b. The parenchyma: its large thin- walled cells : their 

 wall, protoplasm and nucleus : the great number 

 of starch granules in them. 



c. The various patches of sclerenchyma, made up of 

 thick-walled angular cells. 



d. The vascular bundles. Note in each : — 



a. Outside, a single layer of cells with brownish 

 walls, containing no starch granules (endo- 

 dermis or bundle- sheath). 



p. Within the bundle sheath a layer of small 

 parenchymatous cells containing starch (inner 

 or phloem sheath). 



y. Within the last layer comes the bast of the 

 bundle (phloem) consisting of— externally, two 

 or more layers of small rectangular cells with 



