So recently my near-perfect germination rate for Mephisto has been crushed. So I use the recommended tech, damp paper/dvd case, wrapped & placed on my router - this has worked for my dozens of times without a failure. Between two grows I had moved my router vertical on an upper wall and needed a new source of gentle heat. So I used a ridged pet heater, pretty similar temps. But it didn't work, with everything else being the same, it just stopped being successful...over and over again (top row + bottom left + 2-3 more you can't see). Got some rubber bands and went back to the router...100% on the next two (bottom right).
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...temp is a key factor obviously.