Ch. IX. ] LEAVES. 5? 



times become annual plants, losing- their foliage every year. 

 The Passion-flower is a perennial evergreen in southern cli- 

 mates, though annual in ours 



224. Leaves have not that brilliancy of colour which is seen 

 m the corolla or blossom; but the beauty of the corolla, like 

 most other external beauty, has only a transient existence ; 

 while the less showy leaf remains fresh and verdant, after the 

 flower has withered away. 



225. The substance of leaves is so constituted as to absorb 

 the other rays of light, and reflect the green ray ; this colour is, 

 of all others, best adapted to the extreme sensibility of our or- 

 gans of sight. Thus, in evident accommodation to our sense 

 of vision, the ordinary dress of nature is of the only colour up- 

 on which our eyes can, for any length of time, rest without pain. 



226. But although green is almost the only colour which leaves 

 reflect, its variety of shades is almost innumerable. 



"No tree in all the grove but has 'ts charms, 

 Though each its hue peculiar; paler some, 

 And of a wannish gray; the willow such, 

 And poplar, that with silver lines his leaf; 

 And ash far stretching his umbrageous arm-, 

 Of deeper green the elm ; and deeper still, 

 Lord of the woods, the long surviving oak."* 



The contrast between their shades, in forests, where different 

 families of trees are grouped together, has a fine effect, when 

 observed at such a distance, as to give a view of the whole, as 

 forming one mass. 



CHAPTER X. 



Leaves. Appendages. 



227. LEAVES perform a very important office, in sheltering 

 and protecting the flowers and fruit. The fact of their inhal- 

 ing or absorbing air, is thought to have been proved, by placing 

 a plant under a bell glass exhausted of air, permitting the 

 leaves only to receive the influence of airjf the plant remained 



* Cowper. 



t Natural philosophy will inform you of the manner in whicn a 

 glass vessel may be thus exhauste 1 by means of die air-pump. 



224. What is observed of leaves with respect to brilliancy of colour 1 



225. What coloured ray do leaves reflect 1 



22G. What is said of the different shades of green which may be 

 seen in leaves'? 



227 What are some of Tie offices of leaves 1 



