248 PRACTICAL BOTANY 



defined piliferous layer (compare longitudinal sections 

 of the root : below, p. 251.) 



2. The endodermis at the inner limit of the 

 cortex : this is a single layer of cells, having the 

 characteristic marking on the radial walls. Within 

 this lies 



3. The pericycle, a band three or four layers of cells 

 in thickness, immediately surrounds 



4. The central vascular cylinder, in which may be 

 seen 



a. Y-shaped groups of xylem, the fork of the Y 

 directed outwards ; their number varies (3-6) : 

 between the limbs of the fork of each lies a 

 resin-passage. 



&. Groups of phloem, equal in number to the 

 xylern-groups, and alternating with them: 

 these tissues of the phloem are not very 

 easily recognized. 



c. Centrally is a mass of parenchyma, which also 

 extends between the xylem and phloem and 

 separates them from one another. 



II. Cut other sections from an older part of the root, 

 and treat as before. Observe that 



1. The cortex becomes disorganized and brown. 



2. Divisions appear in the outermost cells of the 

 pericycle, forming a layer of cork. 



3. Lateral roots may occasionally be found, origi- 

 nating in the pericycle, opposite the xylem. 



4. The parenchyma lying centrally to the phloem- 

 groups has begun to divide as a cambium-layer. 



III. Cut transverse sections of a thin lateral root 

 (about -% of an inch in diameter) of a full-grown tree of 



