44 THE ART AND PRACTICE OF LANDSCAPE GARDENING. 



and inspection chambers. The direction of main drains should be 

 as closely as practicable that of the lowland, and side drains should 

 follow the slope in parallel lines. The outfall of the main should be 

 above the water level. Ordinarily for a garden the injunctions just 

 made do not so strictly apply. They are modified by important 

 considerations. The walks are generally used for lines of main 

 drainage ; these in most cases traverse ground of steeper inclination 

 than the open land, and there is an obvious variation in the minimum 

 ratio of fall as set out above. It is not advisable to take any main 

 drain nearer to the trunk of an established tree than the limit that 

 is covered by its foliage, because it is not well to alter its former 

 water supply. 



