28 PRACTICAL FORESTRY. 



greater the depth of porous soil, and the greater its 

 power to absorb what the rain-water brings in solution. 

 The soil, too, is cold, for the temperature is always 

 low when there is evaporation ; and evaporation there 

 must be if the water can escape in no other way. 

 Heat cannot be transmitted through water, therefore 

 the sun's rays have no power to penetrate the already 

 filled interstices of the soil. To prove this it is only 

 necessary to ask the forester to try by experiment 

 himself. Let him take the temperature by a thermo- 

 meter six or eight inches below the surface on drained 

 land, and at a similar depth on that undrained, he will 

 find probably a difference of 8 or 10 degrees. 



The expense, however, attaching to extensive drain- 

 age operations is so great as to render it a matter for 

 serious consideration. It is nevertheless for planting 

 not so costly as that for agricultural purposes, and for 

 the simple reason that we require only open drains 

 and sometimes even only grips. Covered drains for 

 planting purposes are not only unnecessary, but are 

 detrimental. Pipes or stone drains will soon be com- 

 pletely choked with root-fibre, and will in a few years 

 render the whole system absolutely useless. In agri- 

 cultural drainage the whole system will often become 

 choked by the roots of trees (which follow the flow of 

 water) finding their way into the drains which pass 

 near. We have found this when draining for planting. 

 When we have been seeking for an outlet we have 

 come accidentally upon mains, or main-feeders, of old 

 agricultural systems which have been so completely 

 choked by root-fibre that the whole of that part 

 dependent upon these drains has been water-logged 



