96 LETTER XXXIV. 



next to be spoken of, from them it is given off to 

 the parenchyma, where it is gradually changed by 

 the complicated processes of digestion, and whence it 

 is retm-ned into the body of the plant. Below the 

 parenchyma run the woody tubes or fibres {fig. 1. g g.)^ 

 which are in this plant short cylinders, but which 

 more generally are very long and flexible ; they com- 

 pose a sheath, 3 or 4 layers thick, to protect the spiral 

 vessels {h.') : highly elastic tubes, capable of unrolling 

 in a spiral direction, and supposed to be connected 

 with the respiration of plants. 



In the accompanying sketch, all the cells of the 

 parenchyma are represented as being in close contact 

 with each other ; but, in reality, there are many open 

 spaces among the cells, arranged in no regular order, 

 and believed to be intended for facilitating the pas- 

 sage of air from one part of the interior of a leaf to 

 another. 



It is far from being my intention to explain any 

 further, in this place, the anatomical structure of 

 leaves. That of Dionsea gives you a sufficiently just 

 idea of the general plan on which they are formed 

 internally ; for more exact information, I must refer 

 you to the higher elementary works on Botany. 



