Compared to a dry day, how would the rate of transpiration be affected on a humid day?
Higher rate of transpiration on a dry day compared to a humid day
Since on a dry day there will be hardly any water vapour in the atmosphere, more diffusion of water vapour would occur from the leaves, thereby ensuring higher rate of transpiration. On the other hand, on a humid day, since there would be water vapour already present in the air, lesser water would diffuse out of the leaves. Hence, lesser transpiration.