14 BULLETIN 495, U. S. DEPARTMENT OF AGRICULTURE. 
or rock below the bottom of the channel. The space built for the 
horizontal screen should be large enough so that coarse sand can be 
placed 12 inches thick on all sides and below the current of the 
stream. This bed can be covered with fine sand or burlap, thus form- 
ing a suction filter which can be occasionally cleaned by removing 
the top covering. The filter always should be covered with an aux- 
iliary burlap or canvas, or the stream shut out when the plant is idle, 
so matter will not settle on the filter and be drawn in when the pump 
is started. 
TYPES OF SPRAY IRRIGATION SYSTEMS. 
Three types of spray irrigation construction have been adopted 
more or less widely for field irrigation. These are: 
(1) Hose and movable-nozzle or movable lines fed from an under- 
sround pipe system and hydrant. 

Fic. 8.—Portable spray equipment used in gardens about cold frames, hotbeds. ete. 
[Luther Burbank’s gardens, Santa Rosa, Cal.] 
(2) Circular nozzles fed from an underground pipe system. 
(3) Overhead spray lines fed from an underground main feed 
pipe. 
The hose and movable-nozzle type is used for the irrigation of 
cold-frame and hotbed crops, garden setting and seed beds, putting 
greens, public parks, lawns, small gardens, greenhouse plants, and in 
some Florida citrus groves. The feeder systems for this type consist 
of main pipe lines and branches which are laid underground to reach 
all portions of the field. At intervals of 50 to 200 feet, ? to 15 inch 
standpipes are brought to the surface and connections for hose made 
by means of shut-off valves threaded at the mouth for the hose 
unions. Lengths of rubber cr canvas hose are used which will reach 

