548 ECOLOGY 



leaves toward light; in so far as the upper surface, regardless of exposure, 

 has the maximum chlorenchyma development, the advantage is evi- 



FlG. 786. — A plant {Nicotiana alata), illustrating a conical habit due to a decrease 

 in the size and in the horizontality of the leaf blades from the base to the apex; note also 

 that the leaves change in shape, being blunt below and pointed above, and that they are 

 arranged in many vertical rows; this plant, like the mullein, illustrates a relative maxi- 

 mum of lighting coupled with a. minimum of shading, and also a progressive increase 

 from the base to the apex of features that protect from excessive transpiration. — Pho- 

 tograph by Fuller. 



dent, but in a great many leaves (as in Lactuca scariola, Populus 

 ddtoides, and Eucalyptus globuius), the greatest development of the 



