188 LIVING PLANTS 



Velvety surfaces 



tion at a time when it is at a minimum in nor- 

 mal leaves. This is an adaptation of great 

 importance in certain regions as is indicated 

 by the great number of species in v\rhich it is 

 found. Begonia, Anthurium, Dracaena, Tra- 

 descantia, and Geranium offer examples of 

 this arrangement. 



The relation of silvery areas to light may 

 be demonstrated if the lower side of a mottled 

 leaf of Begonia or Anthurium is coated with 

 cocoa butter or lard and allowed to cool. If 

 the upper side is exposed to sunlight, the oily 

 substance will melt under the green areas be- 

 fore that beneath the silvery regions is effected . 

 If the experiment is continued until all of the 

 substance is melted and then taken into a 

 shaded place to cool it will be found that the 

 butter opposite the silvery areas remains 

 melted after that on the green portions has 

 solidified. The silvery areas of the leaves 

 carry on food-formation less rapidly than the 

 green regions because of the great obstruction 

 to penetration by light. 



Many leaves exhibit a rich velvety surface 

 that is also due to structural modifications; 

 when combined with underlying layers of 

 color as in Cissus, the effect is very striking. 

 The velvety appearance is due chiefly to the 

 papillose extension of the outer walls of the 

 epidermal cells. The conical and convex 



