HYDROHARMOSE 125 
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* has distin- 
guished 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 
Genistcae; it is also found in Ephedra, many species of Polygonum, 
Lygodesnua, etc. 
3. The rush form. In Heleocharis, many species of Juncus, Scirpus, and 
other Cyperaceae, the stem, which is nearly or completely leafless, is cylin- 
drical 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. 
6. The thorn form. This is typical of many spiny desert shrubs, in which 
the leaves are lost very early, or, when present, are mere functionless scales. 
The stems have an extremely thick cuticle, and the stomata are deeply 
sunken, as a rule. Colletia and Holacantha are good examples of the type. 
1 Lehrbuch der Oekologischen Pflanzengeographie. 2d ed.,196. 1902. 
