*Mycorrhizae* are colonies of fungi symbiotically joined with root systems of plants - each providing unique benefits to the other.
The picture here shows a root system of a seedling on the left prior to inoculation while the shot on the right shows the mycorrhizal symbiosis. The fungi act as "webbing", allowing the plant to grab much more water and nutrients from the surrounding soil. The plant in return provides sugars as a food source for the fungi.
Mycorrhizae provide protection to the symbiotic plant as well. Scientists have found that mycorrhizal fungi provide superb soil remediation by guarding the plant roots from pollutants such as heavy metals and other inorganic toxins. Plants are also more disease-resistant and handle environmental stresses such as drought much better.
When shopping for mycorrhizal fungi, make sure you look for endomycorrhizae - NOT ectomycorrhizae. This is important if you do not like spending money for nothing. While "endos" actually bind internally with the plants roots, "ectos" do not. Certain plant species only benefit from one or the other. Cannabis has been found to only respond to the endomycorrhizae.
I hope this can be a help to those trying to grow the best medicine possible. The Internet is a great tool for further research. Also, message me with further questions and I will be glad to answer them.