ABSORPTION FROM THE SOIL BY PLANTS 239 



and stems that we shall use a stem for our example. If we 



cut & stem with leaves from any of our common trees and 



stand it with the end in red ink for a while, we shall find 



that the ink has ascended the 



stem as water would have 



done, and has left a red 



stain which marks its path 



(fig. 119). This red stain is 



found only in that part of the 



wood which is near the bark. 



This means that the water 



moves up the stem or root in 



the wood which lies next the 



bark, called the sapwood. 



Closer examination of the 

 wood will show that it con- 

 tains numerous large pores, 

 and it is through these that 

 the water travels. These pores 

 may be seen easily in oak 

 wood. The cause of the rise 

 of water in the stems of plants 

 is not wholly understood. 



255. Solids absorbed only 

 when in solution. If there are 

 substances dissolved in the 

 water, these may pass into 

 the plant cells by osmosis, and 

 in this way the plant takes 

 certain mineral substances 



FIG. 119. Ascent of water 



Longitudinal section of a stem, show- 

 ing route of ascent of water : b, bark ; 

 s, sapwood ; h, heartwood ; p, pith. 

 Water ascends principally through the 

 sapwood 



from the soil. Only those 

 substances that will dissolve 

 in the soil water can be absorbed. The absorbed mineral 

 material is transferred through the body of the plant in solu- 

 tion in water and may reach any part of the plant. 



