THE PLANT COVERING OF THE EARTH 327 



water would have done and has left a red stain which marks 

 its path (fig. 159). 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 and which is known as the sapwood. 



Closer examination of the wood will show that it contains 

 numerous large pores, and it is through these that the water 

 travels. These pores may easily be seen in oak wood. The 

 cause of the rise of water in the stems of plants is not 

 wholly understood. 



328. Root surface and transplanting. It is ordinarily impos- 

 sible to remove plants from one place in the soil to another 

 without causing serious disturbances to the root system 

 (fig. 160). Many of the root hairs and smaller roots are 

 broken off, as is usually true of parts of the larger roots. 

 This means that in the new location there will at first be 

 less absorbing surface than the plant previously possessed. 

 Usually some of the roots become dry through exposure to 

 the air and are of no use to the plant, thus further reducing 

 the absorbing surface. 



In transplanting, the branches and leaves do not necessarily 

 suffer the same sort of reduction as the roots do. Since water 

 continues to evaporate from the leaves, and since the absorb- 

 ing surface of the roots is reduced, it is necessary to reduce 

 the evaporating surface of the leaves by pruning. In this 

 way the remaining leaf surface should not make too great 

 a tax upon the absorbing power of the roots before new 

 roots and root hairs are developed. 



