tAYINa OUT. 179 



off the paths and throwiug it on the beds. The adjoining dis- 

 tributing channels act as side-drains during a shower of rain, and 

 protect the paths from being washed away. The irrigation water, 

 as it comes down, is retained, by means of small removeable dams, 

 in the distributmg channels, until the adjoining bed or beds are 

 thoroughly drenched. These dams are simply a square or rectan- 

 gular piece of wood, earthenware, sheet iron, or stone placed across 

 the feed channel in a continuous line with the lower edge of two 

 adjacent distributing ones, and standing just a fraction of an inch 

 below the level of the path on each side, so as to prevent the wa- 

 ter from ever rising high enough to flow over those paths. Oa 

 even open ground the disposition of the beds, paths, and channels 

 would be as represented in Fig. 23, where B B are the beds P P 

 the paths, D D the distributing chennels, F the feed channel, and 

 d d the dams. / 



When the dimension of the nursery in the direction of the 

 length of the beds is too great for a single system of feed channel 

 with its. distributors to perform the irrigation conveniently and 

 efficiently, there must be more than one such system laid out ; and, 

 when this is the case, the feed channels should themselves be fed 

 from a main one running at right angles to them at the highest 

 end of the nursery. 



On hill sides the feed channels on each terrace must obviously 

 receive their water directly from those immediately above them ; 

 and hence, to prevent erosion, it is necessary to pave them, if not 

 along their whole length, at least at both their . extremities. In 

 hilly country flat stones adapted for this purpose are, as a rule, 

 easily obtainable, and both the sides and bottoms of the channels 

 can be protected in this manner at a trifling cost. But a simpler 

 expedient is to form the channel of two planks joined edgewise, 

 as shown in Fig. 24. 



At the upper end of the feed channel on each terrace, a wooden 

 cask may be let into the ground to receive the water falling from 

 above, and of sufficient capacity for any sudden emergency that 

 may arise. Instead of placing a cask, a small stone-lined tank or 

 well may be built. 



If the flooding system of irrigation is employed, the beds must 

 be lower than the paths, and indeed, on the same level as the dis- 

 tributing channels. The water is turned into these channels by 

 damming up with mud the feed channel just below them. It is 

 then admitted into the beds by removing, with the hand or a hoe, a 



