92 IRRIGATION. 



supply may be copious, and the skill of the cultivator is 

 to be exercised in conveying to his field only so much as 

 may be serviceable and no more. But to hit the just 

 mean is a matter of difficulty, if not impossibility, for 

 several reasons. For safety, therefore, in these cases a 

 system of drainage is imperatively needed. Especially is 

 this the case in orchards and vineyards which are subject 

 to so many varieties of blight and mildew, and other dis- 

 eases which have their origin in atmospheric or meteoro- 

 logical conditions. Except in very rare cases, then, it will 

 be imperative that a tile or other drain be laid in the sub- 

 soil at least four feet beneath the surface, between every 

 two rows of distributing canals. This will remove the 

 danger of injuring the plantation by excessive watering. 

 The position of the drains is shown by the dark lines, /, 

 /, /, in figs. 38 and 40, and by the small rings a, a, beneath 

 the surface in figs. 39, 41. 



The roots of trees seek out and follow a supply of water 

 with great avidity. Drain pipes in orchards and gardens 

 have been frequently penetrated by the roots of the trees 

 and completely choked by a dense mass of fibers, eagerly 

 appropriating the water found therein. For this reason 

 the drainage* of orchards by tiles is a somewhat hazardous 

 business. To irrigate the soil of an orchard would tend 

 to keep the roots near the surface where they would re- 

 ceive a sufficiently copious supply of water. "With an 

 abundant supply of water it is not probable that the roots 

 would enter the drains, as the only purpose of their 

 entrance there is to seek moisture. This being supplied 

 as far as necessary upon the surface, the seeming instinct 

 of the roots to enter and choke the drains would have no 

 reason to exist, and would not be likely to occur. The 

 great depth to which the roots of fruit trees and vines 

 penetrate is undoubtedly due in part, if not wholly, to 

 the effort to seek and procure sufficient moisture. The 

 roots of vines have been found spreading at a depth of 



