42 ROOT. [CH. Ill 



The central cylinder is surrounded by an envelope or 

 cylindrical sheath, one cell in thickness, which in section 



FIG. 17. 



PART OF FIG. 13, TRANSVERSE SECTION THROUGH THE ROOT OF Vicia Faba, 

 under a high power. 



c, cortex. p, pith. x, xylem. ph, phloem. 



e, endodermis ; in this specimen the " spindles " on the radial walls were 



only apparent opposite the phloems. 

 p. c, pericycle, which in the bean is of two layers opposite the phloems. 



shows as a ring of cells. This is known as the bundle- 

 sheath or endodermis. It may be recognized because the 

 radial walls, those which separate cell from cell, have a 

 peculiar appearance, due to their being delicately un- 

 dulated, and producing the effect of a dot or spindle. 

 In the root of the bean however this character endodermis 

 is not easily seen. 



Within the endodermis comes another sheath of cells 

 called the pericycle : this is usually a one layered sheath, 

 but in the bean it is in places several cells in thickness. 



