HYDROHARMOSE 123 
intensely xerophytic habitats, and, consequently, it is difficult, if not unde- 
sirable, to place such xerophytes under a particular group. The best that 
can be done is to recognize the types arising from extreme or characteristic 
modification, and to connect the less marked forms as closely as possible 
with these. Halophytes differ from xerophytes only in the fact that the 
chresard is determined by the salt-content of the habitat, and not by the tex- 
ture of the soi!. In consequence, they should not be treated as a distinct 
group. 
168. Types of leaf xerophytes. 
In these, adaptation has acted 
primarily upon the leaf, while 
the stem has remained normal for 
the most part. Even when the 
leaves have become scale-like, 
they persist throughout the grow- 
ing season, and continue to play 
the primary part in photosyn- 
thesis. The following types may 
be distinguished: 
1. The normal form. The 
leaf is of the usual dorsiventral 
character. In place of a reduc- 
tion in size, structural modifica- 
tions 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-con- 
tent by means of a thick cuticle, 
often reinforced by a high de- Fig. 33, Staurophyll of Bahia dissecta, 
velopment of palisade tissue. showing extreme development of palisade 
Such leaves are more or less Kebresard, 3-025 Neat, th, 0< 180; 
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 
S 
01 
