90 VEGETABLES. 



of an iron kettle. It is througli these tliat the sap 

 passes upwards. 



157. If we commence at the extremities of the roots 

 and examine, we shall find that the extremities, called 

 spongioleSj consist only of a bark and a porous sub- 

 stance enclosed. This porous substance extends out 

 to the end of the bark, and is adapted to the absorp- 

 tion of water and watery solutions. Nothing enters 

 a tree or other plant that is not perfectly dissolved, as 

 limpid and transparent as the solution of an ounce of 

 salt or sugar in a gallon of pure water. 



158. If we trace the rootlets from the spongioles 

 upward, we shall find them gradually increasing in 

 size and hardness, and coming together, till instead of 

 millions, there will be only a few ; becoming more 

 and more Like the wood of the trunk ; and before 

 reaching the stem, invested like the tree itself with 

 a double bark, and having like that a pith in the 

 centre. 



159. As we ascend we shall find the branches and 

 twigs becoming more porous as they recede from the 

 stem. Were we to burn the small branches and 

 leaves, we should find them to contain three or four 

 times as much ash as the solid wood, and of the best 

 quality. 



160. The leaf-stems are a continuation of the twig. 

 They are bundles of tubes enclosed in bark ; and 

 these tubes connect with those of the wood below. 



