6 4 ELEMENTARY BIOLOGY. [CHAP. 



4. Examine with -| obj. 



a. The epidermis : its thick-walled cells. 



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

 sac, 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 containing no 

 starch granules (bundle sheath}. These really 

 belong to the parenchyma or ground tissue. 



(3. Within the bundle sheath a layer of small 

 parenchymatous cells containing starch (inner 

 or bast sheatJi). 



y. Within the last layer comes the bast of the 

 bundle (phloein) consisting of externally, two 

 or more layers of small rectangular cells with 

 thickened walls (bast fibres) and then a single 

 row of large thin-walled cells (bast vessels) 

 between which lie smaller thin-walled cells 

 containing starch granules (bast parenchyma). 



8. Within the bast are seen the cross sections 

 of the vessels: note their greatly thickened 

 walls, and large central cavity containing no 

 protoplasm. 



f. Scattered here and there, in the spaces between 

 the angles of the vessels, are small parenchy- 

 matous cells (wood parenchyma) containing 

 starch granules. 

 The wood, or xylem, consists of 8 and e. 



. Treat with iodine : the protoplasm stained 

 brown; the starch granules deep blue 3 render- 



