THE LEAVES 71 



85. Hairs as a protection to the leaf. — The leaves 

 of many species, especially those growing in local- 

 ities subject to very intense sunlight, are often 

 clothed with a dense layer of long wavy or branch- 

 ing hairs, and these serve to ward off the fiercer rays 

 and prevent drying out. The same purpose is also 

 accomplished by the development of a very heavy 

 outer cuticle or wall of the epidermis. 



86. White flowers. — The white colors of flowers or 

 other portions of the plant are due to entirely differ- 

 ent causes. Chief among these is the loose arrange- 

 ment of the cells and the absence of coloring matter. 

 The air between the cells reflects back the light, giv- 

 ing the whitish effect. This may be illustrated by 

 the appearance of a sheet of glass when unbroken, 

 and when crushed or pounded into minute particles. 

 In the first case it shows its natural color and is 

 transparent. When pounded up into a mass of sand- 

 like particles, the light is reflected back from the 

 surface of each, giving the mass a whiti:^h appear- 

 ance. Test the paper-white leaves of any plant you 

 may be able to obtain from a greenhouse and deter- 

 mine to what extent the light penetrates them, as 

 in § 73. 



