82 AGRICULTURE ON THE PACIFIC SLOPE 



fine branches of the veins. And so the water reaches 

 every part of the leaf. 



We think that the leaves draw water up from the 

 root in the same way that the root draws the water 

 from the soil (see page 14). 



In a tree, the water goes up the stem only in the young 

 wood or sapwood. The outside of the stem is so covered 

 with bark that very little water can escape. When a 

 log seasons, the water escapes mostly through the ends. 

 You see this when a green log is placed on the fire and 

 water or steam is forced out by the heat. It.comes out 

 at the end even when the bark is off, because it can easily 

 move lengthwise in the tubes which make up the wood, 

 but not across these tubes (that is, across the grain). 



The experiment in which colored water passes along 

 the vein and into the cells of the leaf shows that only a 

 part of the vein is needed to carry water. The other 

 parts of the vein carry food (starch and protein) from 

 the leaf down into the stem and root. Proteins are 

 substances like white of egg, and are very important 

 foods. The part of the vein in which they move is 

 called the bast. In trees we find the bast just outside 

 the wood. If we cut it away (thus girdling the stem), 

 food cannot pass downward and the roots starve. 

 Branches of grapevines are sometimes partly girdled 

 so that the food may all go into the grapes, instead of 

 leaving the branch and going down into the stem and 

 roots. 



