Compare 亘gen the sun stretching from sky to earth stretching from horizon to horizon stretching all the way accross.
The two lines of the root symbolize the idea that this root extends from the surface of the planet to the depths of the earth it is GRAND IMMENSE
I.ndividual PEI1 EMBRYO
The root 不 hints at the idea of going to the root of the matter, the 月 is the compressed form of 肉 rou ribs meat. So it is the corporeal root i.e. the embryo.