1. _The normal form._ The leaf is of the usual dorsiventral character. In place of a reduction in size, structural modifications are used to decrease transpiration. With respect to the protective feature that is predominant, three subtypes may be recognized. The _cutinized_ leaf compensates for a low water-content by means of a thick cuticle, often reinforced by a high development of palisade tissue. Such leaves are more or less leathery, and they are often evergreen also. _Arctostaphylus_ and many species of _Pentstemon_ are good examples. Lanate leaves, i. e., those with dense hairy coverings on one or both surfaces, as _Artemisia_, _Antennaria_, etc., regularly lack both cuticle and palisade tissue. The protection against water loss, however, is so perfect that the chlorenchym often assumes the loose structure of a shade leaf. _Storage_ leaves usually have a well-developed cuticle and several rows of palisade cells, but their characteristic feature is the water-storage tissue, which maintains a reserve supply of water for the time of extreme drouth. Xerophytic species of _Helianthus_ furnish examples of transverse bundles of storage cells, while those of _Mertensia_ illustrate the more frequent arrangement in which the water tissue forms horizontal layers. 2. _The succulent form._ Many succulent leaves are normal in shape and size, though always thicker than ordinary leaves. Usually, however, they are reduced in size and are more or less cylindrical in form. The necessary decrease in transpiration is effected by the reduction in surface, the general storage of water, a waxy coating, and, often also, by a very thick cuticle. _Agave_, _Mesembryanthemum_, _Sedum_, and _Senecio_ furnish excellent examples of this type. [Illustration: Fig. 34. Diplophyll of _Mertensia linearis_, showing water cells (chresard, 3–9%, light, 1). × 130.] 3. _The dissected form._ The reduction in surface is brought about by the division of the leaf blade into narrow linear or thread-like lobes which are widely separated. The latter are themselves protected by a hairy covering or a thick cuticle, which is often supplemented by many rows of palisade, or by storage tissue. _Artemisia_, _Senecio_, and _Gilia_ contain species which serve as good examples of this type. 4. _The grass form._ Xerophytic grasses and sedges have narrow filamentous leaves with longitudinal furrows which serve to protect the stomata. The furrows are sometimes filled with hairs which are an additional protection, and the leaves often protect themselves further by rolling up into a thread-like shape. The elongated subulate leaves of _Juncus_ and certain _Cyperaceae_ are essentially of this type, although they are usually not furrowed.