240 ELEMENTS OF GENERAL SCIENCE 



256. 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. 

 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 (sect. 128), and since 

 the absorbing surface of the roots is reduced, it is necessaiy 

 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. 



257. Summary. Water is taken from the soil by the roots 

 of plants by means of the process known as osmosis. If there 

 is available water in the soil, it will enter the root as long as 

 the cell sap is a more concentrated solution than the soil 

 water. If it ever happens that this condition is reversed, water 

 may be drawn from the plant. Absorption occurs only at the 

 surface of young root tips and their root hairs. When the 

 root system is seriously disturbed, there is danger of excess 

 of evaporation, which results in death or injury to the plant, 

 unless the evaporating surface is also reduced. 



