156 SCOTCH PINE. 



<?. Next the xylem, large thin-walled mostly empty 



cells. 



/. The phloem j consisting of thick-set, very long 

 cells, with slightly oblique ends, usually crowded 

 with protoplasm and containing large nuclei. 

 Draw. 

 g. The xylem j note 



i. Tracheides like those of the stem but poorly 



developed, with few markings, 

 ii. Spiral vessels like those of the stem ; var- 

 iously placed with respect to the tracheides. 

 Cut the thinnest possible slice from the surface of an old 

 leaf and then cut a thin section from the same place. 

 Mount both with the outer surfaces upward and examine 

 with a high power. Studying the first, the slice of epidermis, 

 note 



17. The arrangement of the stomata. 



18. The two kinds of epidermal cells, those lying near and 

 in a line of stomata and those lying between the lines 

 of stomata ; observe the shapes. In the former note 

 the ridge formed by the upturned edges of the six cells 

 which bound the stoma. 11 If this cannot be readily 

 made out, treat the specimen with potash and observe 

 again in a few minutes. Draw a few cells of each. 



In the tangential section from beneath the epidermis, 

 note 



19. The cut ends of the mesophyll cells ; shape and arange- 

 ment. Draw. 



11 The student should not mistake the peripheral border of the ridge 

 for the outer wall of the six cells. The cells mentioned are quite large, 

 the central ones extending from one stoma to another and the others us- 

 ually half that distance. 



