histogen theory is for root theory ; it was given by hanstein ; root apex and shoot apex consits three layers ;
dermatogen - outer layer of root and responsible for making epidermis and root cap
periblem- inner layer after dermatogen and responsible for making cortex
plerome- innemost layer and responsible for making stele
but in monocot seed there are 4 layers ; calyptrogen , dermatogen , periblem,plerome as calyptrogen is responsible for making root cap and dermatogen epidermis and periblem for cortex,plerome for stele
presence of root cap the root apex is called sub terminal and terminal in shoot apex
quiscent center
these are inactive cell present between dermatogen and calyptrogen ,it also contains less dna ,rna and small nuclei
it was coined by clowes in maize root
