ROOT 105 



II. Cut transverse sections of the root of Hyacinthus 

 orientalis. An old root must be taken, and the sections should 

 be cut as far as possible from the apex. Treat them with 

 potash, and mount in glycerine. Starting from the outside, 

 note successively 



1. The superficial piliferous layer, single cells of which 

 have grown out, here and there, perpendicular to the surface as 

 root-hairs. 



2. Beneath this a layer of cells of larger size with clearly- 

 marked, cuticularised cell-walls : this is the exodermi*. 



3. A thick band of cortical parenchyma, consisting of 

 rounded cells with intercellular spaces : in old roots the outer 

 layers of this tissue become disorganised and distorted. 

 The inmost layer of this tissue differs in structure from the 

 rest, and is called 



4. The endodermis : the radial walls of this layer present the 

 characteristic appearance of a black dot, and are cuticularized. 



5. Within this is a layer of thin- walled cells of the pericycle 

 which immediately surrounds 



6. The central vascular cylinder: two kinds of tissue are 

 specially to be distinguished in this cylinder, viz. 



A Xylem- tissues, easily recognised by their dark lignified 

 walls : they are arranged in a series of groups of indefinite 

 number, which abut externally on the pericycle, and extend 

 inwards, till they meet internally, and form a central mass. 

 The chief constituent are vessels of various form. As may be 

 seen in transverse sections of young roots, the smaller peri- 

 pheral members of each group are formed first (protoxylem), 

 and have spiral or annular thickening ; then successively the 

 larger vessels towards the centre. 



B. The Phloem-tissues, which are groups of elements with 

 small cavity, and bright cellulose walls : they lie between the 

 peripheral groups of the xylem, and alternate regularly with 

 them. 



Apex of the Root. 



It is not easy to cut longitudinal sections of the apex of an 

 ordinary fully developed root without embedding. The 



