The plant tissues inside the cortex. 
• (n.) The central column of parenchyma in a growing stem or root.
(from the article `plant development`) ...proposes that the three principal tissues of the root—vascular cylinder, cortex, and epidermis—originate from three groups of initial cells, or ...
The plant tissues inside the cortex.
Ple'rome noun [ Greek ... that which fills up, from ... to fill.] (Botany) The central column of parenchyma in a growing stem or root.