46 PHENOMENA OF PLANT-LIFE. 



trees, and usually more lucid. While in this young 

 state, the leaves of herbaceous plants often supply re- 

 markably good illustrations of some parts of the inter- 

 nal structure. The tissues are open and succulent ; 

 the general substance is more transparent than later 

 on, and the skin allows of our seeing those delicate 

 little openings, called " stomates," through which 

 moisture is transfused, and communication maintained 

 with the atmosphere. Leaves, in their composition, 

 are threefold. First, there is a delicate skeleton, 

 composed of fibres of woody matter, with sap and air- 

 vessels running alongside ; the interstices of the skel- 

 eton or general framework, are filled up with green 

 pulp, formed of innumerable cells containing fluid; 

 and over the whole, on both sides of the leaf, is 

 spread a transparent skin, that serves to protect the 

 tender subjacent parts. In itself, the substance of 

 the leaf is colorless. The delicious and varied greens, 

 the deep-hued spots, the variegations, the bands, 

 lines, and so forth, of different hues that it presents, 

 come wholly of the sap contained in the cells, which 

 assumes one color or another when the sun shines 

 upon it, according to the matter secreted in it, by the 

 vital economy of the plant. ; The same is true of the 

 petals of flowers. The tissue itself, is totally devoid 

 of color. The blue, scarlet, and yellow, comepf the 

 deposit in the respective cells of fluid, competent to 

 acquire those tints when acted upon by the solar ray. 



