108 COMPOUND OKGANS OF PLANTS. 



or component parts of its flower, as entirely distinct in their 

 derivation and character. A more. extensive acquaintance with 

 floral structure soon, however, discloses the interesting and 

 important fact, that all the beautiful and highly organized parts 

 of the flower are only a series of progressively metamorphosed 

 leaves ; which have assumed these lovely colors and this pecu- 

 liar arrangement and form, in consequence of the peculiar 

 functions assigned them. 



The green leaves on the stem and branches are concerned in 

 the functions of nutrition ; they decompose carbonic acid gas, 

 and, under the influence of solar light, chlorophyl is formed in 

 their cells, (x'>^?°i green, and ^jvj.j.ok a leaf,) so called because 

 it is the substance which gives to the leaves their green hues. 

 The leaves of the stem take their 'peculiar color and form in 

 consequence of their action on the atmosphere ; they take in 

 food from the air, which, in connection with that absorbed by 

 the roots from the soil, contributes directly to the growth or 

 the extension of the parts of the plant. 



The leaves which constitute the flower, on the other hand, 

 are concerned in the functions of reproduction, and are there- 

 fore modified in their structure, form, arrangement, and color, 

 so that they are beautifully adapted to the exercise of these 

 functions. The organs of reproduction which are collectively 

 designated as the flower, are therefore only a peculiar modifica- 

 tion of the organs of nutrition. A flower-bud only difiers from 

 a leaf-bud in having no power of extension. Like the leaf-bud, 

 it is a shortened branch, the axis of which has not been elon- 

 gated, and however the parts of the flower may difier from the 

 ordinary leaves of the plant in appearance, we shall presently 

 show that they may all be referred to the leaf as a type, their 

 nature being precisely the same, and appearance dissimilar in 

 consequence of a difference in the functions assigned them. 



