162 FOREST PLANTIITG. 



from three to four feet aboTe the level of the ground 

 water, although a great many trees send their roots 

 much deeper into the soil. But if the moor is very 

 spongy and porous, there exists such a capillary attrac- 

 tion of the ground water up to the overlaying soil, that 

 with the lowering of the water-table to the stated depth, 

 the necessary drainage and percolation of air through 

 the soil cannot be obtained. It is, therefore, advisable 

 to lay the main ditch, if possible, deep enough so as to 

 bring the water-table to a level with the solid subsoil. 

 The danger that the surface soil, by this arrangement, 

 may be rendered too dry will be avoided, as hereinbe- 

 fore stated, by the erection of proper devices for stop- 

 ping the flow of water at will. 



The main ditch should be laid out in the deepest 

 places of the longitudinal fall of the area, and into this 

 ditch the side-ditches open so as to discharge their water 

 at the most acute angle possible. The side ditches are 

 mostly laid out pretty regular, except if springs or 

 other aqueous spots should be found for the drainage of 

 which special trenches should be opened. If the area 

 to be drained extends more in breadth than in length, 

 especially if the middle part contains an elevation run- 

 ning straight through the middle and is sloping on 

 both sides of the centrum of the area, no side ditches 

 are required, but only several longitudinal ditches, run- 

 ning parallel or nearly so with the main ditch, may be 

 opened, provided they are situated so near to each other 

 as to drain off, completely, the water of the land lying 

 between them. 



The number of side ditches depends upon the quan- 

 tity of the water to be drained off and the condition of 

 the soil, while the depth of the ditches depends upon 

 the elevation of the soil and the quantity of water to 

 be carried by the ditch. Owing to the pressure exer- 



