DESERT VEGETATION. whose nat ural habitats are in di sects. They form one of the three great climatic groups 4.f xerophytes, and show t he t y plea I xerophytic adaptations. whirl' need hut brief statement here. Atost of the adaptations secure reduced transpiration e.g. many plants show reduced leaves—or the leaves may even he wholly absent. as in some cacti: the deehltion: habit is pronounced and its highest expression in animals. where the \dude plant. so to speak, is ,lied during the dry season: anatomical strnetures• such as thick entitles, roats of hair and also wax, protected stomata, etc_ are highly developed. .\daptaf ions which secure increased absorpt inn are often found—e.g. root systems are highly developed— and occur.
the most of all adaptations are storage organs: succulent Ica yes and :Acing are particularly emnition, and there are many plants with fleshy underground stouts (bulbs, tubers, The eonditbins that determine the nature of are associated with the small amount of atmospheric moisture and its seasonal distribution. Most deserts are in semi-tropical regions, and hence the xerophy tic conditions are accelerated by intense heat and hiss of water by evaporation rather than by drainage often gives rise to alkaline soils, which still further intensify the xerophytic characters. See lia,toeurrEs.
The vegetation of deserts is characterized by monotony rather than poverty. there being hut few species that van endure the severe conditions. 'Flit' plants are scattered so that the soil gives the landseape tone. In comparing desert plants with alpine and arctic plants., many erologieal differences are seen: the most striking are the deciduous and succulent habits—habits particu larly adapted to regions where drought is the result 01 heat. Floristically. deserts are noted for their endemism (11.v.I. agreeing in this with alpine, but disagreeing with arctic- vegetation. The endemism of deserts is due in part to their geographic isolation; mountains and other bar riers commonly cut of deserts on all sides and prevent effective migration. However. another factor which favors endemism is the intense modification that desert plants have undergone as a result of the severe conditions. See XERO