136 A PINE. 



14. Sections running in various directions through bordered 

 pits. 



15. The very tapering ends of tracheids. 

 II. THE LEAF. 



Make a cross-section of the needle-leaf, mount and note the 

 following regions: 



1. The outer heavy-walled epidermal and strengthening 

 region. 



2. The mesophyll region, made conspicuous by the presence 

 of chlorophyll. 



3. The vascular bundle region, composed of light-colored cells 

 and surrounded by a distinct row of cells, the bundle- 

 sheath. 



4. Make a diagram showing the form of the cross-section, and 

 the relative position and extent of each region. 



Study the details of each region as follows: 



5. Epidermis. 



a. The thick cuticle. 



b. The epidermal cells, their very thick walls and the 

 peculiar thickening within the cells. 



c. At somewhat regular intervals the stomata, each stoma 

 consisting of: 



i. An outer chamber which appears as a depression 



in the cuticle and epidermal layer. 

 ii. An inner chamber lying within the chlorophyllose 



tissue immediately below the outer chamber, 

 iii. A narrow opening connecting the two chambers, 

 iv. At the sides of the outer chamber are two promi- 

 nent epidermal cells, and immediately beneath 

 these are: 



v. Two smaller guard-cells distinguishable by con- 

 taining chlorophyll. 



6. The incomplete layer of cells immediately below the epi- 

 dermis, the sderenchyma or hypoderma. Observe: 



