5. _The needle form._ This is the typical leaf of conifers, in which a sweeping reduction of the leaf surface is an absolute necessity. The relatively small water loss of the needle leaf is still further decreased by a thick cuticle, and usually also by hypodermal layers of sclerenchyma. 6. _The roll form._ Roll leaves are frequently small and linear. Their characteristic feature is produced by the rolling in of the margin on the under side, by which an almost completely closed chamber is formed for the protection of the stomata which are regularly confined to the lower surface of the leaf. The upper epidermis is heavily cutinized and the lower one often protected by hairs. This type is found especially among the genera of the _Ericales_, but it also occurs in a large number of related families. 7. _The scale form._ Reduction of leaf surface for preventing excessive water loss reaches its logical culmination in the scale leaf characteristic of many trees and shrubs, e. g., _Cupressus_, _Tamarix_, etc. Scale leaves are leathery in texture, short and broad, and closely appressed to the stem, as well as often overlapping. =169. Types of stem xerophytes.= In these types the leaves are deciduous early in the growing period, reduced to functionless scales, or entirely absent. The functions of the leaf have been assumed by the stem, which exhibits many of the structural adaptations of the former. Warming[15] has distinguished the following groups: 1. _The phyllode form._ The petiole is broadened and takes the place of the leaf blade which is lacking. In other cases, the stem is flattened or winged, and it replaces the entire leaf. This type occurs in _Acacia_, _Baccharis_, _Genista_, etc. 2. _The virgate form._ The leaves either fall off early or they are reduced to functionless scales. The stems are thin, erect, and rod-like, and are often greatly branched. They are heavily cutinized and palisaded, and the stomata are frequently in longitudinal furrows. This type is characteristic of the _Genisteae_; it is also found in _Ephedra_, many species of _Polygonum_, _Lygodesmia_, etc. 3. _The rush form._ In _Heleocharis_, many species of _Juncus_, _Scirpus_, and other _Cyperaceae_, the stem, which is nearly or completely leafless, is cylindrical and unbranched. It usually possesses also a thick cuticle, and several rows of dense palisade tissue. 4. _The cladophyll form._ In _Asparagus_ the leaves are reduced to mere functionless scales, and their function is assumed by the small needle-shaped branches. 5. _The flattened form._ As in the preceding type, the place of the scale-like leaves is taken by cladophylls, which are more or less flattened and leaf-like. _Ruscus_ is a familiar illustration of this form.