570 A TEXTBOOK OF BOTANY [Cn. XIV 



vailing, but not desert dryness, like the Levant, forms like 

 Butcher's Broom (Fig. 140) are common. EVERGREEN 

 GROUND PLANTS ; on the same principle as the preceding ; 

 typified by Wintergreen. Allied are evergreen trailers like 

 Periwinkle, Ground Pine, and the evergreen Ferns. CARPET 

 MOSSES ; with dense-tufted, upright, low stems from creeping 

 protonemata (page 487), forming dense turf; occurring also 

 as epiphytes, and on barren plains. Allied is the form of the 

 Carpet Liverworts. CRUSTACEOUS LICHENS; the associa- 

 tions of Fungi and Algae, able to resist desiccation but to 

 absorb water quickly when available (page 461) ; fitted to 

 cling to bare surfaces, and hence extending into barren sit- 

 uations, including tree trunks and bare rocks. BUNCH 

 GRASSES; forming compact radiating heads on dry plains 

 (page 63). SAGE BRUSH SHRUBS; deliquescent, but -with 

 persistent vertical leaves which revive at moist times, as in 

 the Sage Brush of our deserts. Allied are the leafless shrubs 

 of dry climates (Fig. 138). RESURRECTION PLANTS; 

 rosette-form, curling inward to a ball when dry, but expand- 

 ing flat with moisture; typified by Selaginella lepidophylla 

 (page 505) and the Rose of Jericho (Fig. 257). SPINY 

 SHRUBS; more or less green on the stems and the great 

 spines ; found commonly on deserts in Asia and Australia. 

 ROSETTE LEAF SUCCULENTS ; with compact, rotund leaves 

 storing water and food, as in the African Mesembryanthemum 

 (Fig. 44). ROSETTE PERENNIALS; stemless, with leaves 

 brought to a compact whorl on the ground ; typified by the 

 rock-dwelling Sempervivum (Fig. 131) and by many ever- 

 green herbs. RADIATE LEAF SUCCULENTS ; a head of stout, 

 stiff-pointed leaves, swollen towards the base and storing 

 water and food, as in Century Plant, Aloe, and Eremurus 

 (Fig. 232). TUFT TREES ; radiate heads of long, stiff, linear 

 leaves in a crown on a columnar trunk ; typified by Cordy- 

 line (Fig. 35) and Yucca, common on American deserts. 

 STEM SUCCULENTS; stems short and thick, often rotund, 

 filled with water and food, thick-epidermed, bearing the 



