154 THE ELEMENTS OF VEGETABLE HISTOLOGY 



absorption of dialyzable materials. The epidermis 

 is seldom more than one layer of cells in thickness, 

 and the cells are not strongly cutinized as are those 

 of the green portions of the plant. As illustrated in 

 Plate 54, epidermal cells in sectional view appear in 

 more or less rectangular or, oblong forms. They are 

 rather thin walled, excepting upon exposed surfaces, 

 which may show slight thickening. On surface view, 

 which is the most frequently had when examining 

 powdered materials, epidermal cells show rectangular 

 and polygonal forms. 



Hypodermis. — The hypodermal layer occurring in 

 primary roots is immediately within the epidermis; 

 and the individual cells are usually slightly colored. 

 This tissue may be one or more layers of cells in thick- 

 ness, but the number of cell layers seldom exceeds 

 five. The hypodermal tissue is partly a covering 

 tissue; it normally assumes this function in certain 

 plants and may assume it in others if the epidermis 

 is injured. Hypodermal cells, as seen in transverse 

 section, are usually angled and possess uniformly 

 thickened walls. In longitudinal sections and in 

 powdered materials, these cells appear rather long and 

 similar to fibers, except for the fact that their end 

 walls are blunt or square. 



Cortical Parenchyma. — The primary cortex is 

 bounded on the outside by the hypodermis and on 

 the inside by the endodermis. The cortical cells 

 represent the original parenchymatic tissue of the 

 periblem region, and undergo but little change during 

 the growth of the root. The cortex is usually several 

 layers of cells in thickness; and within these cells 

 much of the nutrient material of the plant is stored. 



