212 PRACTICAL BOTANY. 



side of the leaf. The bark portion, or phloem, is situated 

 towards the lower or outer, rounded side of the leaf. 



Mount in Schultze's solution thin cross sections of 

 leaves of different species of Pine, cut after imbedding in 

 paraffin or celloidin. 1 Comparing with Fig. 134, locate on 

 a drawing of the section all the parts mentioned above. 

 The whole section should be drawn in outline, but it will 

 be sufficient if the details are drawn in only half of it. 

 In what portions of the section is the cellulose lignified? 

 Notice under high power that the epidermis is composed 

 of three layers : the cuticle is the outer, thin and trans- 

 parent coating ; the other two coatings are thick walled. 

 Can you make out cracks running from the centers of the 

 cells outward through these walls? Find places where 

 the section passes through a stoma; observe the guard 

 cells, and the air chamber into which the stoma opens. 



Trace the hypoderma around the section. Is the num- 

 ber of rows of cells of which it is composed constant? 

 How many rows do you find? Observe the hypoderma 

 beneath a stoma ; what do you notice ? 



Tie a number of fresh leaves together with thread 

 tightly. Imbed the bundle in pith and cut cross sections. 

 Mount in water and examine the mesophyll. Observe 

 the abundant chlorophyl. Determine if it bears starch. 

 Notice the folded walls of the cells. 



Observe the thin- walled parenchyma within the bundle 

 sheath. Does it bear chlorophyl and starch? What is 

 the prevailing shape of the cells as seen in cross section ? 



Draw under high power the xylem and phloem as seen 

 in the section which was mounted in Schultze's solution. 

 Also draw a portion of the bundle sheath. What do you 

 find to be the contents of the cells of the bundle sheath in 

 a section from a fresh leaf ? 



1 For methods of preparation, see the author's "Practical Methods 

 in Microscopy," Chap. VII. 



