ACTION OF LEAVES. 37 



CHAPTEE IV. 



ACTION OP LEAVES 



Their Nature, Structure, Veins, Epiderviis, Stomates. — 

 Effect of Light. — lyigestion or Decomposition of 

 Carbonic Acid. — Insensible Perspiration,. — Forma- 

 tion of Secretions. — Fall of the Leaf. — Formation of 

 Buds by Leaves. 



59. A LEAF is an appendage of the stem of a plant, 

 taving one or more leaf-buds in its axil. In those 

 cases where no buds are visible in the axU, they are, 

 nevertheless, present, although latent, and may be 

 brought into developement by favourable circum- 

 stances. As this is a universal property of leaves, to 

 which there is no known exception, it follows that all 

 the modifications of leaves, such as scales, hooks, 

 tendrils, &c., and even the floral organs, hereafter to 

 be described, have the same property. 



60. Considered with respect to its anatomical struc- 

 ture, a leaf is an expansion of the bark, consisting of 

 cellular substance, among which are distributed veins. 

 The former is an expansion of the rind ; the latter 

 consist of woody matter arising from the neighbour- 

 hood of the pith, and from the liber. As the tissue 

 forming veins has a double origin, it is arranged in 

 two layers, united firmly during life, but separable 

 after death, as may be seen in leaves that have been 



