Actinobacteria are a hyphae-producing soil bacteria that, in appearance and behavior, have more in common with soil fungi. The spores of Actinobacteria have a distinctive, earthy smell we often associate with rainfall. The smell comes from a compound, geosmin, which translates to "earth smell". The human nose is exquisitely sensitive to geosmin, able to detect it at concentrations down to 10 parts per trillion.

"Teaming with Microbes", by Jeff Lowenfels and Wayne Lewis. Foreword by Elaine Ingham. Strong soil science orientation. Well organized. Extensive index. Valuable guide to labs and suppliers. Looking forward to actually reading it.