too PLANT GEOGRAPHY 



Benth. and Hook, with Myrica Faya Ait. From this 

 to nearly 6000 feet is the belt of Conifers and Heaths ; 

 and above this again the Retama (Spartocytisus nubi- 

 genus Webb and Bert.). It is noteworthy that on the 

 lofty volcanic heights of these islands, where botanists 

 first traced altitudinal zones in detail, there is none of the 

 so-called " Scandinavian " invasion of Glacial times. 



The Mediterranean and Levantine Region is remarkable 

 for the dense scattered thickets or maquis (Italian 

 macchia) of fragrant glandular and often prickly shrubs 

 with rigid leaves, such as Myrtus communis L., Pistacia 

 Lentiscus L., and Laurus nobilis L.; for the Olive (Olea 

 europcea L.), Evergreen Oaks (Quercus llex'L., Q. Suber 

 L., etc.); for numerous sweet-scented Labiates; and 

 for the Fan-palm (Cham&rops humilis L.), which is wild 

 on both sides of the Mediterranean. The Date-palm, 

 though grown in Italy, belongs to the oases of the 

 Saharan region. The desert districts of Syria and 

 Palestine, with their few Tamarisks and spinous Acacias, 

 form a transition to the next region. 



The Steppe and Central Asian Region stretches from 

 the Danube to the upper Amoor and from the Volga to 

 the Persian Gulf and the Himalayas. Throughout this 

 immense area there prevails a regular succession of three 

 marked seasons, a long and severe winter with snow, a 

 short spring, and a rainless summer. The vegetation is 

 consequently typically xerophytic with bulbs, spines, or 

 dense coverings of hair. Salt plains are frequent with 

 characteristic " halophytic " vegetation, especially Che- 

 nopodiacecz, such as the bushy Saxaul (Haloxylon 

 ammodendron Bunge). Shrubby species of Astragalus 

 and the genera Rheum and Ferula are also well repre- 

 sented (Fig. 8). These wind-swept plains and plateaux 

 are unsuited to any tree-growth. 



The Prairie Region of North America, in many respects 

 a similar area, is a treeless plain with an extreme climate, 

 short spring rain, and dry summer. The prevalent west 

 wind from the Pacific condenses all its moisture on the 

 Rockies, and the rivers that do originate from its rainfall 

 flow in deep canons, so as to be of little use for irrigation. 

 In its northern portion this region is a true grass steppe, 

 parched in summer: in the south-west, the salt or 

 " alkali " desert, with its Sage-brush (Artemisia triden- 

 tata Nutt.) and the Creosote-scrub (Larrea mexicana 



