You know some fungi more by how they affect their host than by how the fungus itself looks. For example, at the right you see a cross section of a broccoli stem afflicted with a stem rot fungus. Here you don't really see the fungus, but with a little experience you know that the fungus is there. In the picture you can see that the bottom part of the stem is firm, green and healthy, but a brown, mushy and very stinky dead zone is working its way down the stem.
In fact, the stem already has deteriorated so much that the entire top of the plant has fallen over and become detached from the stem! You see a few green sprouts gamely trying to survive, but their days are numbered. The unseen fungus is sending its hyphae into more and more living cells and as they die they turn brown, mushy and smelly. I think that the name of this fungus is Thanatephorus cucumeris but I'm not sure. This fungus really hurts my garden crops of broccoli and cabbage. It's hard to get rid of this fungus because its reproductive structures persist in the soil for years!