3. _Reduction of leaf._ The transpiring surface of a plant is reduced by decreasing the number of leaves, by reducing the size of each leaf, or by a change in its form. In so far as the stem is a leaf, a decrease in size or a change in shape brings about the same result. The final outcome of reduction in size or number is the complete loss of leaves, and more rarely, of the stem. Such marked decrease of leaf area is found only in intense xerophytes, though it occurs in all deciduous trees as a temporary adaptation. Changes in leaf form are nearly always accompanied by a decrease in size. Of the forms which result, the scale, the linear or cylindrical leaf, and the succulent leaf are the most common. Leaves which show a tendency to divide often increase the number of lobes or make them smaller. 4. _Epidermal modifications._ Excretions of wax and lime by the epidermis have a pronounced effect by increasing the impermeability of the cuticle, and, hence, decreasing epidermal transpiration. It seems improbable that a coating of wax on the lower surface of a diphotic leaf can have this purpose. The thickening of the outer wall of epidermal cells to form a cuticle is the most perfect of all contrivances for decreasing permeability and reducing transpiration. In many desert plants, the greatly thickened cuticle effectually prevents epidermal transpiration. In these also the cuticle is regularly developed in such a way as to protect the guard cells, and even to close the opening partially. An epidermis consisting of two or more layers of cells is an effective, though less frequent device against water loss. When combined with a cuticle, as is usually the case, the impermeability is almost complete. Hairs decrease transpiration by screening the epidermis so that the amount of light and heat is diminished, and the access and movement of dry air impeded. While hairs assume the most various forms, all hairy coverings serve the same purpose, even when, as in the case of _Mesembryanthemum_, they are primarily for water-storage. Hairs protect stomata as well as epidermal cells: the greater number of the former on the lower surface readily explains the occurrence of a hairy covering on this surface, even though absent on the more exposed upper side. In some cases, hairs are developed only where they serve to screen the stomata.