64 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 sderenchyma, 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. 



ft. Within the bundle sheath a layer of small 

 parenchymatous cells containing starch (inner 

 or bast 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 

 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. 



c. 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, render- 



