botany - What factors affect the rate of transpiration in plant leaves?

I'm trying to get my head around factors which affect transpiration in leaves.

For example, how would applying petroleum jelly to the surface of plant leaves affect their rate of transpiration?

I get that it's basically going to decrease the trasnpiration rate because the stomata will be covered, but I'm not sure about these parts:

• How would it affect the rate of transpiration if only the top surface was covered?


• How would it affect the rate of transpiration if only the bottom surface was covered?

Also, I think I'm right in saying that increasing wind / applying a fan to plant leaves will increase the transpiration rate, but why?