HYACINTH. KOOT. 119 



5. The central Vascular cylinder. This consists 

 of groups of tissue of two sorts. 



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 

 pericambium, and extend inwards, till they meet in- 

 ternally, and form a central mass. The chief con- 

 stituents are vessels of various form. 



As may be seen in transverse sections of young roots, 

 the smaller peripheral members of each group are formed 

 first (protoxylem), and have spiral thickening ; then 

 successively the larger vessels towards the centre. 

 Between the peripheral groups of the xylem, and 

 alternating regularly with them may be seen 



B. The Phloem-tissues, which are groups of ele- 

 ments with small cavity, and bright cellulose walls. 



II. Cut radial longitudinal sections of the same 

 root : treat in the same way, and observe the several 

 tissues above described. The whole root will be seen 

 to be composed of similar elements to those found in 

 the stem. 



Transverse sections should also be made of the root of the 

 Maize. The main features of the section are the same, though the 

 structure differs in several minor points from that of the root of 

 Hyacinth. Thus, in the Maize root there is a parenchymatous 

 pith, and the xylem abuts directly on the bundle-sheath. 



In these sections may be found the point of junction of lateral 

 roots with the main root. It may be seen that the former ori- 

 ginate from the pericambium of the main root, and that they 

 break through the bundle-sheath, cortical tissue, and epidermis ; 

 also that their vascular tissue is continuous with that of the main 

 root ; the activity which produces them begins opposite a 

 phloem-mass of the main root, and not opposite a xylem-mass, 



