ne 
assimilation being taken over by the two connate spiny pro- 
phylls. The whole plant forms a spiny ball sometimes as 
large as 30 centimetres in diameter and of a grey colour. 
(See fig. 66). 
Under the Summer-plants should also be grouped a red 
Lichen, Lecidea decipiens which in some places is common 
on the surface of the loess. 
The structure of the Summer-phanerogams will be dealt 
with later (chap. 13), when the different types of desert-plants 
are described. Here it is only necessary to give some of the 
more important features. The species which grow in the most 
favourable localities, where the ground-water is not too deep, 
are generally these with relatively the richest foliage: Tama- 
rix, Halimodendron, Prosopis, Peganum, Zygophyllum, Pluchea, 
Inula, Alhagi have all distinctly green leaves and flat, with 
the exception of those of the Tamarix. None of them however 
have much foliage, nor does it cover the stems. In A/hagi 
only the oldest leaves persist, so that the upper shoots look 
like leafless spiny branches. 
The plants of the dry desert may be grouped as follows: 
Succulents, Bracteole-Succulents or Leaf-Succulents, the last 
including Salsola Arbuscula, subaphylla, rigida and verrucosa, 
Reaumuria; leafless Stem-Succulents such as Haloxylon, Ana- 
basis and Calligonum; deciduous shrubs like the species of 
Astragalus where other organs take over the work of assimi- 
lation; and finally plants with narrow leaf segments coated 
with hairs (Artemisia). All the species from the dry clay- 
desert belong to very xerophytic types, many have in addition 
a halophilous stamp (cylindrical assimilation - organs with 
aqueous tissue in the middle). In a case such as we are now 
considering it may be difficult, perhaps impossible, to dis- 
tinguish between the xerophytic and the halophytic; which 
structural adaptations are due to desiccation and which to 
salinity of the ground-water can only be positively determined 
by experiments. 
The usual aspect of the clay-desert in summer is a flat 
or slightly undulating surface, brown and dry, here and there 
with slight incrustations of salt, bare or scantily covered with 
scattered xerophilous plants which are herbs or small shrubs 
