You can find exact information from a horticulturist speacializing in this flower or a more general manual covering the effects of soil temperature on microbiological flora as well as the horticultural response. In general, snapdragons and many other plants are susceptible to fungal infections during germination.
Bacterial infections are less of an issue.
Many of the fungi are sensitive to soil conditions, and can be stopped by increasing salt content, lowering soil pH and so on. However, in the case of snapdragons this has the unfortunate effect of killing the plant as well. Thus, soil temperature seems to be the horticulturalist's best answer to keeping fungal infections to a minimum. Copyright 1998-1999, Room103 group. Don't steal this.