Observations of the leaf characters of the desert perennials, as
shown in November, offer some points of interest, especially since
there had been no rain for a year previous to the visit. As would be
expected, the leaf-habit is various, ranging from scale-like or none
to fair size. Several species appear to be evergreen, including
_Artemisia herba-alba_, _Capparis spinosa_, _Echium humilis_,
_Fagonia bruguieri_, _Gymnocarpon_ sp., _Haloxylon articulatum_,
_Helianthemum sessiliflorum_, _Henophyton deserti_, _Herniaria
fruticosa_, and _Salsola_. Certain plants probably, as _Henophyton_,
are facultative evergreens, retaining the leaves if the season is
moist and dropping them if it is excessively dry; several of this
genus were seen without leaves, but with green stems. (See, also,
figs. 39, 40, and 41.)
Some idea of the variation in size of the leaves of a single species,
as well as the average size of the leaves, will be had from the
results of a few measurements. The leaves of _Henophyton deserti_
range in length from 2 to 3.1 cm., and in breadth from 0.2 to 0.5
cm. The average length of 12 leaves from a single branch 7 inches
in length was found to be 2.82 cm.; the average breadth was 0.35
cm. On another branch, 23 cm. long, were 35 mature leaves which
averaged almost exactly the size of those just given. Since these
leaves are rather numerous and of good size, it will appear at once
that the species has a relatively large leaf-surface, even if the
area can not be stated more definitely. (Fig. 30.)
The evergreen shrub _Capparis spinosa_ has the largest leaves of
any plant native to the Ghardaia region, and probably of southern
Algeria. Its leaves are bilateral and nearly round and are placed
upright on the branches; a series of 29 leaves from one branch 33
cm. long varied from 2 to 3.2 cm. in length and slightly less in
width, the average being, length 2.9 cm., breadth 2.2 cm.
_Euphorbia guyoniana_ has a deciduous leaf-habit. Its leaves are
rather small but numerous. A shoot 22 cm. long bore 40 leaves
varying in length from 1.5 to 2.1 cm. and in breadth from 1.2 to
2.0 mm., with the average length and average breadth 1.7 cm. and
1.6 mm. respectively.
It is worth noting that the surface of the leaves, as shown by
inspection, is, possibly, most often smooth, as, for example, in
_Capparis_, _Henophyton_, and _Haloxylon_. Dense hairiness is an
exception among the species seen, _Lithospermum callosum_ being
the only plant striking in this regard.