152 PRACTICAL BOTANY. 



single layer of cells, having the characteristic marking 

 on the radial walls. Within this lies 



3. The Pericambium, a band three or four layers of 

 cells thick. This immediately surrounds 



4. The central Vascular cylinder, in which may be 

 seen 



a. Y-shaped groups of Xylem elements, the fork of the 

 Y directed outwards ; their number varies (3 6). Be- 

 tween the limbs of the fork of each lies a resin-passage. 



I. Groups of Phloem elements, equal in number to 

 the xylem groups, and alternating with them. N.B. 

 These tissues of the phloem are not very easily 

 recognised. 



c. Centrally is a mass of parenchyma, which also 

 extends between the xylem and phloem masses, 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 disorganised and brown. 



2. Divisions appear in the outermost cells of the 

 pericambium, forming a layer of cork. 



3. Lateral roots may occasionally be found, origi- 

 nating in the pericambium, 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 -j\- of an inch in diameter) of a full-grown tree 

 of P. sylvestris ; mount some sections in glycerine, 

 others in Schulze's solution. Observe successively, 

 starting from the periphery of the section : 



1. Withered remnants of the Cortex. This may, 

 however, have been already completely thrown off. 



