VII.] THE BRACKEN FERN. 63 



/3. Within the sheath-cells a layer of small paren- 

 chymatous cells containing starch. 



7. Within the last layer come the bast-cells ; small 

 rectangular cells with slightly thickened walls, 

 and arranged in several rows. 



B. Within the bast layer, come one or more rows 

 of larger thin-walled cells, 



e. The cross sections of the vessels : their greatly 

 thickened walls, and large central cavity con- 

 taining no protoplasm. 



Scattered here and there, in the spaces between 

 the angles of the vessels, are small parenchyma- 

 tous cells containing starch-granules. 



e. Treat with iodine : the protoplasm stained brown ; 

 the starch-granules deep blue, rendering some of 

 the cells quite opaque and almost black-looking, 



5. Cut a thin longitudinal section of the stem and 

 examine with 1 inch and then with -J obj. Make out 

 the various tissues described in 3 and 4. 



a. The epidermis and parenchyma, much as in the 

 transverse section. 



b. The sderenchyma is seen to be made up of greatly 

 elongated cells, tapering towards each end. 



c. The vascular bundles ; note in them 



a. The sheath-cells and parenchyma much as in 

 the transverse section. 



ft. The vessels: elongated tubes presenting cross 

 partitions at long intervals. Two forms of 

 vessel will be seen, viz. scalariform vessels, 



