CAUSES OF CONTINUED ENTRANCE 109 



Two things permit the solutes to keep on entering. The 

 picture on this page {Figure 37) represents the region in 

 which these things occur. In the center of this picture 

 are the wood cells of the vascular system ; these cells are 

 dead. When the water and the solutes enter these cells, 

 they begin to move together. The solutes move along 



Fig. 37. — The region in which water and solutes enter the plant body. They 

 move through the cells of the cortex by osmosis. These cells are alive. The 

 cells of the xylem are dead. When the water and solutes enter the xylem they 

 move in a mass together, not by osmosis. 



with the water just as sugar dissolved in tea would move 

 with the tea if you poured it from the cup. But before 

 reaching the wood, that is between the root-hairs and the 

 wood cells, the water and the solutes have to move through 

 the living cells of the cortex, and through these they move 

 by osmosis, and not together as one mass. 



Now it appears that the sap current, ascending through 

 the wood cells, carries away solutes from the cells of the 

 cortex which border it. Then, to satisfy the laws of 



