Hartig nets in soil produce by

A Hartig net is a complex of fungal hyphae found in the intercellular spaces between the cortical cells of a root. It may cover the plant cell to the extent that the cell has no contact with other root cells.
Hartig net in the soil is produced by ectomycorrhiza. Ectomycorrihizas is a form of symbiotic relationship that occurs between a fungal symbiont and the roots of various species. The hyphae in the Hartig net penetrate and grow in a transverse direction to the axis of the root, and form a network between the outer cells of the root axis.