HORSE-CHESTNUT ROOT 155 



xylem, so as to be able to recognize it in the older 

 roots. 



7. The groups of primary phloem, equalling in 

 number those of the xylem : this tissue is not well 

 marked. 



8. Narrow bands of parenchyma separating the suc- 

 cessive groups of phloem and xylem : subsequently 

 these cells are the seat of origin of the cambium. 



VI. Cut similar transverse sections from a part of a 

 root which has recently turned brown, and has produced 

 lateral roots : comparing with the above sections, note 

 the following changes : 



1. The piliferous layer and cortex have turned brown, 

 and will often be separated from the central cylinder 

 by rupture of the radial walls of the endodermis. 



2. The cells of the pericycle will be found undergoing 

 periclinal divisions, which ultimately result in the 

 formation of a layer of cork. 



3. The groups of primary xylem as before, but united 

 at the centre so as to form a star-shaped mass, with no 

 central pith : the groups of primary phloem alternating 

 with those of primary xylem, as before. 



4. Divisions may be seen in the cells intervening 

 between the xylem and phloem, which indicate the 

 position of the cambium. 



5. If lateral roots be present, they originate from 

 the pericycle. 



VII. Cut transverse sections of still older portions 

 of the root, about T V of an inch or more in diameter 

 treat with chlor-zinc-iodine, which brings the starchy 

 medullary rays into prominence. Now examine care- 

 fully the central mass of tissue, and recognize the 



