XV.] THE BRACKEN FERN. 453 



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

 in water and examine with i 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. T\it 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 {bundle 

 sheath). 



p. Within the bundle sheath a layer of small 

 parenchymatous cells containing starch {inner 

 ox 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 



