This suzanne simard book talks a lot about "mycorrhizal" fungi quite a lot ie those that form a symbiotic relationship with a plant.
Typically the plant gives the mushroom the products of its photosynthesis ie sugars. And the mushroom gives thd plant access to water.
But the big that stuck out for me is that there's 2 types, one where the mushroom mycelia kinda latch onto the roots and thd exchange happens cos they're touching one another, they're sort of wrapped around one another.
But in another type, the fungus actually penetrates the root walls of the tree, and grows inside it like a parasite.
Yeah, endophytic fungi are pretty cool. Have you ever tripped on morning glory or Hawai'ian baby woodrose seeds? They contain compounds identical to those found in ergot (i.e. LSD precursors), but it's recently been discovered that these compounds aren't produced by the plants themselves, but by fungi that 'infect' them:
Heritable microorganisms play critical roles in life cycles of many macro-organisms but their prevalence and functional roles are unknown for most plants. Bioactive ergot alkaloids produced by heritable Periglandula fungi occur in some morning glories (Convolvulaceae), similar to ergot alkaloids...
'Infect' is in quote marks, since the fungus is apparently beneficial to the plants (maybe by making them poisonous to insects that would otherwise eat them), even though it's closely related to ergot, which is unequivocally a parasite.
I gave my dad one of the two copies of Sheldrake's book I received for Christmas. He says he read about a third of it or something, and then decided he knew quite as much about fungi as he really needed to.