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LEAVES. 
Caducous , such as fall before the end of summer. 
Deciduous , falling at the commencement of winter, this is the case with 
most vegetables, as far as 30° or 40° from the equator. 
Persistent, or permanent, remaining on the trees amidst the changes of 
temperature : as the leaves of the pine and box. 
Evergreen, preserving their greenness through the year ; as the fir-tree 
and pine, and generally all cone-bearing and resinous trees ; these change 
their leaves annually, hut the young leaves appearing before the old ones 
decay, the plant is always green. 
In our climate the leaves are mostly deciduous, returning in 
the autumn to their original dust, and enriching the soil from 
which they had derived their nourishment. In the regions of 
the torrid zone, the leaves are mostly persistent and evergreen ; 
they seldom fade or decay in a less time than six years; but 
these same trees, removed to our climate, sometimes become an- 
nual plants, losing their foliage every year. The Passion flow- 
er is an evergreen in a more southern climate. 
Leaves with respect to Colour. 
Leaves have not that brilliancy of colour which is seen in the 
corolla or blossom ; but the beauty of the corolla, like most 
other external beauty, has but a transient existence ; while the 
less showy leaf remains fresh and verdant, after the flower has 
withered away. 
The substance of leaves is so constituted as to absorb all the 
rays of light, except green ; this colour, is, of all others, best 
adapted to the extreme sensibility of our organs of sight. Thus, 
in evident accommodation to our sense of vision, the ordinary 
dress of nature is of the only colour upon which our eyes can 
for any length of time rest without pain. 
But although green is almost the only colour which leaves 
reflect, their 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 grey ; 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. 
* Cowper. 
Colour — Why they are mostly green — Different shades iD plants, to what 
owing? 
