NATURE OF PLANTS 47 



ing the jar in water until the soil is wet. Further watering is not 

 required until the jar sounds hollow when tapped a matter of 

 several days. So gardens and lawns should be thoroughly soaked 

 during the night. The ordinary sprinkling only moistens the sur- 

 face and leaves the soil in a worse condition for holding the mois- 

 ture than before, because the hard crust draws up the water to the 

 surface where the dry air readily evaporates it. The top soil 

 of the garden should be kept loose by raking or hoeing, since the 

 loose soil can not withdraw water from the root and it thus acts 

 just as a mulch of straw or leaves or as the grass of the fields in 

 retaining the water in the soil. In this connection the fact must 

 not be lost sight of that a very considerable portion of water in 

 the soil can not be withdrawn by evaporation. It is often sur- 

 prising to note how plants continue to flourish during a drought 

 when the earth is sun-baked. This is because the films of water 

 about the soil particles cannot be withdrawn by the dryest and 

 hottest air. The bulk of this water, however, is available to the 

 roots, which, branching through the soil, send out root hairs in 

 all directions and so absorb practically not only all the water in 

 their neighborhood, but owing to the capillary action of the soil, 

 water is drawn to them from the adjacent soil at a distance of 

 from four to six feet. 



23. Extent of the Root Surface. It may seem surprising that 

 the roots are able to take up the large volumes of water that are 

 lost daily through transpiration. The spread of the root, how- 

 ever, is much more extensive than we think, usually quite equal 

 to that of the branches, so that the absorbing portion of the root 

 is beneath the drip of the branches or exposed to the rains and 

 dews. Furthermore, when we come to add together the lengths 

 of the numerous rootlets, the extent of the total root system is 

 still more surprising. The total length of the roots of an oat 

 plant has been estimated at 154 feet; of a corn plant, at 1320 feet; 

 and of a squash plant at fifteen miles. These roots in ordinary 

 soil reach a depth of from three to five feet, but in dry regions 

 much greater depths are attained; for example, alfalfa 31 feet 

 and mesquite 60 feet. The most important increase in the ex- 

 tent of the root system is due to the root hairs, 480 having been 



