ABSORPTION OF WATER 183 



in water through the surfaces of their stems and leaves as well 

 as through their roots, but the crops of the farm and garden 

 and all ordinary land-plants absorb all the water which they 

 require from the soil by means of their roots only. 



When the soil in a pot in which a plant is growing is allowed 

 to become dry the plant begins to droop and wilt, and no amount 

 of syringing or even immersion of the leaves and stems in water 

 will completely revive and sustain the life of the plant so long 

 as the soil is kept dry. 



In good well-drained soil, the chief amount of rain which falls 

 upon it sinks through into the subsoil, but a certain amount 

 remains behind in the form of more or less thin films of water 

 surrounding each solid particle of which the soil is composed. 



In such soil some water is retained in the minute spaces 

 present in it, and a certain amount of water travels upward from 

 the subsoil by capillarity into these spaces in the upper layers 

 of the soil. Good well-drained soils, while thus retaining an 

 adequate supply of water, allow a free penetration and circula- 

 tion of air within them. Only in water-logged soils totally 

 unsuited to the growth of ordinary farm and garden crops are 

 all the spaces between the component particles of the soil 

 completely filled with water, and air excluded. 



Soon after the appearance of the primary root from a seed 

 secondary roots spring from it, and from these new roots arise, 

 so that the soil becomes penetrated in all directions by fine 

 rootlets, near the ends of which numbers of root-hairs are 

 developed. The growing rootlets push their way through the 

 small crevices in the soil and the root-hairs are brought into 

 close contact with the small particles of soil and with the films 

 of water surrounding the latter. 



Formerly the absorption of water was supposed to take place 

 through the root-caps which were termed ' spongioles ' ; experi- 

 ments, however, have shown that plants are able to absorb all 

 the water they need when the root-caps are exposed to the air 



