PLANTS AND WATER 



39 



ABSORPTION OF WATER 



Roots. Since the water in good soils is all in the mem- 

 branes surrounding the soil particles, it is the water in 

 these membranes which the roots must be able to take 

 up. As a matter of fact, they are never able to take it 

 all, but die from dryness while the soil still holds some 

 water. To be able to take the water 

 from the soil particles, the roots of 

 the plants must come into contact 

 with these particles as completely 

 as possible. And since it is ob- 

 viously the surface of roots which 

 can absorb water, they need to have 

 a great deal of surface. To get a 

 great surface, and to reach all the 

 soil particles possible, most plants 

 have a great number of fine roots. ni; 

 By actual measurement, the total 

 length of the roots of one squash 

 plant was twenty-five kilometers. The coconut is nota- 

 ble for having few fine roots; yet one tree may have 

 more than six hundred thousand absorbing tips. 



Root Hairs. Hut even the finest roots of plants are 

 usually not fine enough to keep plants well supplied 

 with water, and so the roots have special absorbing 

 structures, the root hairs. These are tubular outgrowths, 

 each from a single epidermal cell. They have exceed- 

 ingly thin walls, and so can grow into the finest chinks 



Root liairs in 

 contact with particles 

 of s-oil 



