VEGETABLES. 89" 



have space to say but little, as the more important 

 matter of their decay and return to the soil is yet un- 

 touched. 



153. With regard to the structure of plants, I will 

 refer you to our common trees, not exactly as a sam- 

 ple for others, but as affording some data from which 

 you can reason, and observe for yourselves both re- 

 semblances and differences. 



154. The stem of a tree consists of woody fibre, 

 formed around the pith, an inner bark around that, 

 and an outer bark around the whole. 



155. The pith is a spongy, soft substance, com- 

 mencing far down in the roots, coming together at the 

 base of the stem, then continuing upward, dividing 

 and subdividing itself in the branches and twigs, till 

 it reaches their extremities. Some mysterious con- 

 nection seems to be kept up between the pith and the 

 inner bark, by means of a set of pores, running from 

 the pith outward every way, like the spokes of a 

 wheel. 



156. The roots may be regarded as the extension 

 of the stem downwards, and the branches uS its ex- 

 tension upwards. The wood is not as compact as 

 many may suppose. Its more solid parts even consist 

 of an immense number of tubes running side by side 

 from the lower to the upper extremities of the tree, 

 varying in size in different parts, and each one lined 

 with a substance different from itself, like the tinning 



