Saisons are fun.
I don't think they were generally spontaneous fermentations, though, at least not most of the time. On the top of p. 110 of Farmhouse Ales, the author states that Brewers repitched yeasts from previous batches, as was the conventional practice for all beer around then. This was certainly a slurry of pure brewers' yeasts, wild yeasts, and probably even lactobacillus, etc.
Yeast is everywhere. You can culture it from straight out of the air pretty much anywhere.
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