Can someone enlighten me on this. How do the trichomes spread onto the leaves? Do they actually spread from the inner of the bud and work their way outward on the tops of the leaves? Or do they actually grow up through the leaves?
Here you go. This article should answer a bunch of your questions. Inside the Trichome- By Bubbleman and Jeremiah Vandermeer and I'll post a couple of inspirational photos.
Trichomes can grow anywhere on the plant. They grow predominantly in and around bud sites (calyxes), but they also grow on leaves (even upper fan leaves and stems sometimes). Good high quality MJ grows thick trichomes on the leaves around the bud sites (in my experience). I won't bother propagating any strain/genotype that doesn't have thick trichomes on the bud leaves.