^20 



PLANT LIFE. 



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



profile position when the illu- 

 mination becomes too intense. 

 These positions, liy pilacing the 

 leaf surface oblique to the ch- 

 rection of the light ravs, reduce 

 the amount of e\aporation \'ery 

 considerably. 



437. 4 Coverings, consist- 

 ing of li\ing or dead scale- 

 leaves, sti[uiles, leaf-bases or 

 entire leaves, reduce transpira- 

 tion by obstructing the free ex- 

 change of air, or by holding 

 Hater and so keeping moist the 

 siirlaces they co\"er. 



438. 5. Structural modifi- 

 cations. — These niav oc( ur 

 either in the epidermis or some 

 internal tissues. (1?) 'i'he epi- 

 dermis may greatly reduce evap- 

 oration b)- the formation of 

 hairs in such profusion as to 

 form a cover lor the surface 



Hairs in- 

 main axis; ran^ellaiT scales just peep- tended to protect from evap- 



ing from between placental scales or i v^ ^ ^ I 



oration are usually dead and 

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

 white, and the surface seems hoar\', or woolly, or silky. 

 Hairs in the form of scales which o\-erlap reduce the rate of 

 evaporation by covering the stomata (fig. 365). Further 

 adaptations of the epidermis arc to be found in the pres- 

 ence of a thick cuti( le (fig. 367); the «"ater-proofing of 

 the whole of the outer wall of the cjiidermis; the develop- 



Flt-.. :i5S. — Shoot of larch, with 

 cone; showing needle-shaped leaves (fj.rj^^ -,61-^64). 

 on dwarf branches; scale leaves on ^ ^ «-' 0^1 



■arjiellarj 



:tween p 

 cone. Natural size. — After Kerner. 



