144 THE BEAUTIES OF NATUBE chap. 



and j^j. In the first the leaves are generally 

 broad, in the | arrangement they are elliptic, 

 in the y% and more complicated arrangements 

 nearly linear. The Willows afford a very 

 interesting series. Salix herbacea has the ^ 

 arrangement and rounded leaves, Salix caprea 

 elliptic leaves and f, Salix pentandra lancet- 

 shaped leaves and |, and S. incana linear leaves 

 and a j% arrangement. The result is that 

 "whether the series consists of 2, 3, 5, 8, or 13 

 leaves, in every case, if we look perpendicu- 

 larly at a twig the leaves occupy the whole 

 circle. 



In herbaceous plants upright leaves as a 

 rule are narrow, which is obviously an advan- 

 tage, while prostrate ones are broad. 



AQUATIC PLANTS 



Many aquatic plants have two kinds of 

 leaves ; some more or less rounded, which 

 float on the surface ; and others cut up into 

 narrow segments, which remain below. The 

 latter thus present a greater extent of surface. 



