Gh. 1X. | LEAVES. 57 
tres 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 prilliancy of colour which is seen 
in 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 its 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 air;} the plant remained 
* Cowper. - 
¥ Natural philosophy will inform you of the manner in which a 
glass vessel may be thus exhausted by means of the air-pump. 
224. What is observed of leaves with respect to brilliancy of colour? 
225. What coloured ray do leaves reflect 2 
226. What is said of the different shades of green which may be 
seen in leaves? 
227. What are some of the offices of leaves? 
