Many mushrooms have a distinctive odor, though it is sometimes hard to put your finger on what it's like. Also, some of the references are obscure ("coal tar"?) and it's hard to allow for the power of suggestion. Here is a brief discussion of the more popular mushroom odors.
Tricholoma odora story
Image of Russula mutabilis from Gotthold Hahn (1883) Der Pilz-Sammler oder Anleitung zur Kenntnis der wichtigsten Pilze Deutschlands und der angrenzenden Laender
Many mushrooms, for example, have a sweet odor that is often described (and will be, in general, here) as almondy: like marzipan or the odor of almond extract. That is, it's supposed to be almondy, but the odor of different collections has been called (when I tried to tell my co-hikers that it was almondy) "hazelnut" and "orangy", and they convinced me in both cases. The almondy smell is typical of mushrooms in section Arvenses of the genus Agaricus, and section Laurocerasi of the genus Russula.
The boletes in section Bicolor have an odor that to me is very sweet, like cotton candy; to Gary Lincoff, the same mushroom smells spicy, like curry powder. And we've both been able to convince others of the correctness of our perception. Probably it's just a genetic thing, like the flowers that smell different to different people. So you need to identify the mushroom for the first time from visual characteristics, and then see what it smells like to you.
This is a smell that has been described variously as a smell of maple syrup, burnt sugar, curry powder or fenugreek. Some people have even tried to use distinctions between the smells listed above as a feature in identifying mushrooms. This seems fraught with peril to me, since there seems to be a genetic factor to the smell - - it just smells different ways to different people.
In fact, I believe that both this and the sweet-spicy smell are cocktails of smells, only some of which have the genetic factor (almost everyone can detect the sweet component, for example). It's perfectly possible that the make-up of the cocktail varies consistently between certain species, but if you can't smell the component that varies, you can't use the key that makes use of it.
Another popular odor is " phenolic". This is used as an indicator for the poisonousspecies of Agaricus. The most exposure any of us have had to the smell of real phenol is in the thick white paste one uses in kindergarten. If you can still remember that, you're doing very well! Most of us end up re-learning it by finding an Agaricus that smells really bad, and all of a sudden the smell of library paste comes back to us...
