320 



PLANT LIFE. 



instead of the surfaces. (See ^| 285.) Others assume a 

 profile position when the illu- 

 mination becomes too intense. 

 These positions, by placing the 

 leaf surface oblique to the di- 

 rection of the light rays, reduce 

 the amount of evaporation very 

 considerably. 



437. 4 Coverings, consist- 

 ing of living or dead scale- 

 leaves, stipules, leaf-bases or 

 entire leaves, reduce transpira- 

 tion by obstructing the free ex- 

 change of air, or by holding 

 water and so keeping moist the 

 surfaces they cover. 



438. 5. Structural modifi- 

 cations. — ■ These may occur 

 either in the epidermis- or some 

 internal tissues. (a) The epi- 

 dermis may greatly reduce evap- 

 oration by the formation of 

 hairs in such profusion as to 

 form a cover for the surface 

 (figs. 361-364). Hairs in- 

 tended to protect from evap- 

 oration are usually dead and 



filled with air. Reflecting light from many points, they look 

 white, and the surface seems hoary, or woolly, or silky. 

 Hairs in the form of scales which overlap reduce the rate of 

 evaporation by covering the stomata (fig. 365). -Iuirther__ 

 adaptations~ot the epidermis are to be found in the pres- 

 ence of a thick cuticle (fig. 367); the water-proofing of 

 the whole of4he outer wall of the epidermis; the develop- 



. — Shoot of larch, with ripe 

 showing needle-shaped leaves 

 on dwarf branches ; scale leaves on 

 main axis ; carpellary scales just peep- 

 ing from between placental scales of 

 cone. Natural size. — After Ke 



