DRAINAGE. 601 



inches below the surface, is much drier than the corresponding 

 zone on bare fallow land, the opposite being the case as regards 

 the uppermost layers of soil, which are protected by the leaf- 

 canopy of the trees from insolation and the drying action of 

 winds, while the moss and dead needles retain much moisture 

 near the surface of the ground. Investigations in Russia by 

 Ototzky, and in France by Henry, have confirmed this in the 

 strongest possible manner, and for other trees besides spruce. 



/. Season. 



In countries with heavy snowfall, where the snow remains 

 lying on the ground throughout the winter, the soil is wettest 

 in the spring, after the snow has melted. 



In the south-east of England, the soil is probably wettest 

 from November till March, but dries up rapidly after the 1st of 

 March till July, owing to the scanty rainfall and the prevalence 

 of dry east winds. 



3. Protective Rules. 



(a) In mountain regions, and in very rainy districts, such as 

 the boggy parts of Ireland, where the formation of swamps is 

 to be feared, forests should be maintained and be completely 

 stocked, and shadebearing conifers are best for the purpose. 



The spruce probably exercises the greatest action in draining 

 soil, the superficial roots of this species acting like drain-pipes; 

 the Scots and Austrian pines are also very useful in suitable 

 localities, and retain a large proportion of the atmospheric 

 precipitations on their needles and branches. 



(b) Marshy plants should be removed from the ground, and 

 in damp, low-lying places the circulation of the air should be 

 increased by clearings, thinnings, pruning and removal of 

 undergrowth. 



(c) All ditches and watercourses in forests should be kept 

 open, and at least once a year should be cleared of water- 

 plants, dead leaves and mud. 



(d) Mountain torrents should be regulated. 



SECTION IV. DRAINAGE. 



A superfluity of water in the soil can be thoroughly rectified 

 only by drainage. Before, however, undertaking such a work, 



