24 THE STORY OF PLANT LIFE 



xerophytes have become modified to meet the exi- 

 gencies of the habitat. They are frequently stunted, or 

 dwarf, and may adopt the rosette or the cushion habit. 

 The leaves also are adapted to meet these conditions. 

 The surface is reduced, the stomata are fewer. The 

 leaves are often fleshy. Many are evergreen, to 

 effect economy of materials. The surface is screened 

 by hairs, scales, etc., to prevent drying of the surface. 

 The cuticle is often leathery, or waxy, to prevent the 

 accumulation of water outside, and loss of water. 

 The air-spaces are not so numerous. The leaf is 

 thicker and the cells are filled with mucilage in 

 fleshy types. Corky and lignified tissues filled with 

 air help to retain the water. 



The leaf is often needle-like, overlapping, small, 

 thick, heath-like, with the margin inrolled, juncoid, 

 long, smooth, circular and inrolled. The leaves may 

 be modified and the stalks may become phyllodes, or 

 shoots may have the same function as leaves, as in 

 switch-plants, or where the leaves are scales with 

 cladodes as in Butcher's Broom, or where plants 

 develop thorns and spines, e. g. gorse. The leaves of 

 heaths are overlapping and turn their edges to the 

 light. 



In contrast to the modifications of xerophytes to 

 meet a lack of water, are those of water-plants to 

 meet a superabundance of water. Water-plants do 

 not transpire. They obtain their air and light and 

 their food from the water. 

 Aquatic plants have large air-spaces in order that 



