TRANSPIRATION. 151 



ganic matter, the food of plants and the food also 

 of animals. 



The path of the ascent of the crude sap is 

 through the woody portions of the plant. The 

 woody tissues of the roots carry the water from 

 cell to cell to the fibrovascular bundles of the stem ; 

 it then rises through all the branches and twigs 

 till it reaches the leaves. Each leaf has a woody 

 framework, which divides again and again, till it 

 makes a network of fibres, on which the green 

 tissue (parenchyma) is supported. The most deli- 

 cate fibrils of this woody framework are in close 

 contact with the cells of the leaf which communi- 

 cate with the outer air, and the water which has 

 been brought hither from the roots escapes into 

 the atmosphere. 



We can see that it must be the wood which con- 

 ducts the water, by looking at old trees, whose 

 trunks are hollow and whose bark has also been 

 destroyed around the base of the tree. This is 

 especially striking in old olive trees, which often 

 are not only hollow and destitute of bark, but are 

 pierced and broken, so that the upper part of the 

 tree looks as if it were mounted on stilts, and is 

 only connected with the ground by woody tis- 

 sue. Yet these olive trees are healthy, bring forth 



