Lecture XIX. 



153 



the base or attachment of the root. From the sides of this cell 

 are formed flat segments which produce the cortex and conducting 

 tract. Its base forms segments which give origin to an irregular 

 cap-like mass, the outer cells of which have little cohesion and 

 simply form a lubricating substance to facilitate the forward passage 

 of the growing root through the soil. 



The leaves are essentially organs for exposing the photosyn- 



FIG. 37. Aspidium Jilix-mas, lower epidermis, x 300. a, epidermal cell 

 with scattered chloroplasts ; b, guard-cells with crowded chloroplasts ; 

 c, stoma. 



thetic cells to the light and air. The leaf-stalk and rachis have 

 the function of supporting these cells in a suitable position and 

 maintaining their communications with the rest of the plant. 

 The leaf-stalk is a rigid tube formed of the outer sclerenchymatous 

 layers of fundamental tissue continuous with that of the stem. 

 This tube is filled with parenchymatous fundamental tissue con- 

 tinuous with the soft fundamental tissue of the stem, but differing 

 from it in that its cells contain chloroplasts. Embedded in this 



