LEAVES. 



ous trees ; these change their leaves annually, but the young 

 leaves ajDpearing before the old ones decay, the plant is always 

 green. In our climate the leaves are mostly deciduous, return- 

 ing in autumn to their original dust, and enriching the soil 

 from which they had derived their nourishment. In the re- 

 gions of the torrid zone, the leaves are mostly persistent and 

 evergreen ; they seldom fade or decay in less than six years ; 

 but the same trees*, removed to our climate, sometimes become 

 annual plants, losing their foliage every year. The passion- 

 flower is an evergreen in a more southern climate. 



59. The GKEEN COLOR of leaves is owing to a coloring matter 

 called Clilorojphyl (from cliloros^ green, 2Ci\A jpJiyUon^ leaf), which 

 floats in minute globules in the fluid of cells accompanied by 

 starch grains. The green color becomes lighter or deeper ac- 

 cording to the quantity of chlorophyl and the aggregation of 

 cells. Leaves have not that brilliancy of color which is seen 

 in the corolla or blossom ; but the beauty of the corolla has 

 only a transient existence ; while the less showy leaf remains 

 fresh and verdant after the flower has withered away. The 

 substance of most leaves is so constituted as to absorb all the 

 rays of light excej)t green ; this color 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 color upon which our eyes, for 

 any length of time, can rest without pain. But although green 

 is almost the only color which leaves reflect, the variety of its 

 shades is almost innumerable. 



" 1^0 tree in all the grove but has its charms, 

 Though each its hue peculiar ; 'paler some, 

 And of a wannish-grar ; the willoio 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 oa^-."* 



The contrast between their shades, in forests, where difterent 

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

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

 forming one mass. A small quantity of carbon, united to 

 oxygen in the vegetable substance, and acted upon by light, is 

 said- to give rise to the various colors of plants.f If this theory 

 be correct, the different shades of color in plants must be 

 owing to the difterent proportion in wdiich the carbon and 



* Cow per. 



t This idea coincides wilh the supposition, that the green color of leaves is changed to brown by the 

 loss of an acid principle ; that the petals of flowei-s change from purple to red by an increase of acid. 

 The base of this acid is oxygen. 



59. Chlorophyl. 



