192 NATURAL THEOLOGY. 



putrefaction, and the soft part washed away, there 

 remains an elegant skeleton of wood, which retains 

 the form of the leaf, and which is perfectly well 

 suited to support its delicate organization. It is 

 the same substance which, when accumulated and 

 condensed, gives form and strength to the roots 

 and branches of the oak ; and these, though fan- 

 tastic and irregular in their growth, preserve a 

 mechanical principle of strength as obvious to the 

 ship-builder, in the knees of timber, as in the 

 delicate skeleton of the leaf. Lord Bacon speaks 

 of "knee-timber, that is good for ships that are to 

 be tossed." The woody fibre, though not directly 

 engaged in the living functions of the tree, is yet 

 essential for extending the branches and leaves 

 to the influence of the atmosphere, and by its 

 elasticity under the pressure of the wind, giving 

 what is equivalent to exercise for the motion of 

 the sap. A tree opposed to winds and to a severe 

 climate is dense in its grain, and the wood is 

 preferred by the workman to that which is the 

 growth of a milder climate. 



We cannot miss seeing the analogy of the 

 woody fibre with the bones of animals. Bones 

 are firm, to sustain the animal's weight, and to 

 give it form. They are jointed, and move under 

 the action of muscles ; and this exercise promotes 

 the activity of the living parts, and is necessary to 

 health. But let us first observe the structure of 

 some of the lower animals. It will be agreeable 

 to find the hard material, thougli always appro- 



