The petroleum jelly had a greater effect when it was spread on the lower surface
than when it was spread on the upper surface since in the lower surface area there is more stomata than the upper surface area which means the rate of loss of water in the lower part is greater than the upper part due to the presence of more stomata in the lower part than the upper part, and if we spread petroleum jelly on the lower part this means that the great number of stomata in the lower part will be blocked and this will mean that less loss of water will occur than if we spread petroleum jelly on the upper part due to the presence of less stomata than the lower part, this shows that if we cover the lower part with petroleum jelly it will have greater effect than the upper part.