PIN US AUSTRIACA, OR P. LARICIO. 137 



o. The number of rows of cells in thickness in different 

 parts of the section, and their compactness. 



b. The especial adaptation for strengthening the leaf at 

 its angles. 



c. The small circular (in section) cell cavity, and the 

 heavy walls with pore-pits. 



7. The mesophyll. 



a. The shape of the cells, the average number of rows 

 between the hypoderma and the bundle-sheath. 



b. The infoldings of the wall, dividing the cavity into 

 recesses. Observe the position of the most prominent 

 of these infoldings in the outermost row of mesophyll- 

 cells. Observe occasionally (usually near a stomatal 

 cavity) branched cells. 



c. In fresh specimens the abundant chlorophyll. 



d. The resin-ducts; compare their structure with that 

 of the ducts in the stem. Notice the thick walls of 

 the sheath-cells. 



8. The vascular bundle region. 



a. The bundle-sheath; shape and contents of the cells. 



b. The two masses of small cells, the two vascular bundles. 

 Each bundle is distinctly divided into a xylem and 

 phloem area. A partially developed resin-duct some- 

 times appears in the xylem. 



c. Surrounding the bundles, the parenchyma, some of 

 which may form radial rows running through the 

 bundles as medullary rays. 



d. Make a diagram of the section and draw a narrow strip 

 across it, showing in detail each kind of tissue. 



III. THE MICROSPOROPHYLL. 



From a cone that was collected just before the pollen-grains 

 were shed, remove some of the stamens and observe: 

 i. Their general form. 



