MAIZE. APEX OF ROOT. 121 



pith, while its peripheral part develops into the vascular 

 ring. Note rows of larger cells, which may be traced 

 back as continuous with vessels of the xylem. In the 

 central portion of the plerome are intercellular spaces, 

 which appear black in sections from fresh material, 

 being filled with air. 



2. Surrounding the plerome is a broad band of tissue 

 with intercellular spaces, which appear as above. This 

 is the Periblem, which is the formative tissue of the 

 cortex. 



3. Outside this is a single layer of cells somewhat 

 elongated radially, and with a thick outer wall : this is 

 the Dermatogen or formative tissue of the epidermis. 



If the section be accurately median it will be possible 

 to trace (2) and (3) upwards, till, immediately above 

 the apex of the plerome, they merge into a single 

 layer of cells : thus the formative tissue from which 

 the epidermis and cortex are derived, is represented at 

 the apex by a single layer of cells. 



4. Outside the dermatogen, at the apex of the root 

 will be found another formative tissue, the cells of 

 which divide parallel to the surface of the dermatogen : 

 this is the Calyptrogen layer, which is formative of 

 the tissues of the Root-cap. The latter appears as a 

 mass of parenchyma, covering the whole apex of the 

 root : the outer cells of it will be seen to be undergoing 

 disorganisation, and mucilaginous degeneration of the 

 cell- walls. 



