XEROPHYTES 
167 
other xerophytes the leaves are more or less twisted at the 
base, so as to place their edges upwards. The phyllodes of 
Acacia (« q.v .), &c., attain the same end in a different way. 
Another similar arrangement is seen in the isobilateral leaves 
of Iris, Narthecium, Phormium, &c. (p. 49). 
In addition to the reduction of transpiration obtained 
by these methods many xerophytes store up water to last 
them through the dry season, and thus become more or less 
succulent. The water is usually stored in aqueous tissue , 
consisting of large colourless living cells, often below the 
upper epidermis of the leaf, as in Aeschynanthus, Peperomia, 
&c. More extreme development of the storage-function 
leads to the true succulent plants. The storage may be in 
the leaf, as in most Crassulaceae, many Liliaceae (e.g. Aloe, 
Haworthia, Gasteria, &c.), Aizoaceae {e.g. Mesembry- 
anthemum), Drymoglossum, Agave, Fourcroya, Sansevieria, 
&c., or in the stem, as in Cactaceae, many Asclepiadaceae 
{eg. Stapelia, Huernia, Sarcostemma, Ceropegia, &c.), Eu- 
phorbia sp., Senecio sp., Sarcocaulon, Salicornia, &c. In the 
leaf-succulents the leaves are thick and fleshy, are usually 
closely packed, and provided with thick cuticle, sunk sto- 
mata, &c. In the stem-succulents the leaves are reduced to 
scales or thorns ; the stems are fleshy and of various shapes, 
and are often grooved. Many succulents, especially the 
Cacti, are able to survive very protracted drought. It is 
difficult to dry specimens for the herbarium. They do not 
resist long-continued wet weather easily, but soon decay. 
Xerophytes show in general the characters of sun-plants, 
eg. a very well-developed palisade-tissue, thick leaf, &c. 
The wood is usually hard, dry, and brittle. Many, especially 
the desert species, are thorny, eg. Alhagi, Acanthophyllum, 
Acantholimon, Astragalus, Euphorbia, Cactaceae, &c. The 
thorns are probably useful as protections against animals, 
especially in the succulent species. 
Bud-protection against extreme heat and excessive tran- 
spiration is well marked in most xerophytes. In the succulent 
forms, eg. Mesembryanthemum, Aloe, Agave, Cactaceae, the 
bud is usually deeply sunk among the leaves or in a groove 
or pit in the stem, so that it is almost completely covered. 
Other protections, of the various kinds already described, 
occur in other species. The dry-season buds of non- 
