PLANT ORGANS AND ORGANISMS 153 



Histology of a Typical Woody Monocotyl Stem. The stem of the 

 Greenbrier, a woody monocotyl, will here be considered. In trans- 

 verse section passing from periphery toward the center the following 

 structural details will be noted: 



i. Epidermis, of a single layer of epidermal cells whose outer walls 

 are strongly cutinized. Cutin is a wax-like substance which forms 

 a protective coat to the epidermis, preventing the evaporation of 

 water, the ingress of destructive parasites, and injury from insects. 



FIG. 79. Cross-section of cornstalk stern; a, epidermis; b, cortex and 

 c, ground tissue. {After Stevens.) 



2. A cortex, composed of about ten or twelve layers of thick- walled 

 parenchyma cells, the outer two or three layers of which are termed 

 hypodermis. 



3. An endodermis, wavy in character and composed of endodermal 

 cells whose brownish walls are strongly suberized. 



4. A sclerenchymatous cylinder sheath composed of somewhat 

 separated masses of sclerenchymatous fibers and undeveloped fibro- 

 vascular bundles of the closed collateral type. 



5. A central matrix of strongly thickened parenchyma cells in 

 which are scattered, irregularly, numerous closed collateral bundles. 

 Small starch grains will be found in the parenchyma cells. Examine 

 a representative bundle, and note the two very large tracheae and 



