120 PKACTICAL BOTANY. 



as is usually the case (cf. Dicotyledons). This is to be connected 

 with the fact that the xylem-groups in the Maize (and in most 

 Grasses) abut directly on the bundle-sheath. 



Apex (punctum vegctationis). 



It is not easy to cut longitudinal sections of the apex 

 of an ordinary fully developed root without embedding. 

 The arrangement of the meristematic tissues is, how- 

 ever, the same in young as in old roots ; it is therefore 

 more convenient, and quite as successful, to cut longi- 

 tudinal sections of the apex of the young lateral roots, 

 which are to be found growing horizontally out of the 

 nodes of the Maize plant. Or, if fitting material for 

 this be not at hand, longitudinal sections may be made 

 of the radicle of the embryo, in seeds which have been 

 previously soaked for several hours in water. 



Adopting one of the above methods, cut longitudinal 

 median sections of the apex of the root. Treat them 

 for ten minutes with dilute potash : neutralise with 

 acetic acid, and mount in glycerine. 



N.B. The section must be accurately longitudinal 

 and median, i.e. the section must include the organic 

 axis of the root, around which the several tissues are 

 symmetrically arranged. 



In a median section the following arrangement of 

 tissues will be visible. 



1. A central mass of tissue, clearly defined laterally, 

 and rounded off at its apex, which is at some distance 

 below the external apex of the root : this is the 

 Plerome cylinder. If this tissue be traced back into 

 the older part of the root it will be found that its 

 central part is continuous with the parenchymatous 



