WATERING, HEATING, VENTILATING AND SHADING 163 
THEORETICAL DISCHARGE OF 100 Nozzles 1n U. S. GALLoNns 
PER MINUTE 
The No. 1 outdoor nozzles and the No. 3 greenhouse nozzles are 
the sizes most generally used 
cr Head — Type nozzles ————__, 
Pounds Feet Greenhouse No.2 Greenhouse No. 3 
5 11.55 11.5 176 
10 23.1 16.3 25.1 
15 34.7 19.9 30.8 
20 46.2 23.1 85.4 
25 57.8 25.8 38.6 
30 69.3 28.4 43.3 
35 80.9 30.6 46.9 
40 92.4 32.6 . 50.2 
The nozzle lines in the greenhouse may be supported 
by special hangers’ provided for the purpose. Holes in 
the pipe for the brass nozzles are made by a special drill- 
ing machine. It is not a difficult matter to install an 
overhead system of watering, and the manufacturers are 
always pleased to give instructions on any point which 
may not be fully understood. Whenever a pressure of 
10 pounds or more can be obtained, it is possible to op- 
erate the overhead system of watering, though a higher 
pressure makes a finer spray. In fact, practical growers 
prefer a pressure of not less than 25 pounds, and 40 
pounds is better. 
Temperature.—The proper temperatures for the various 
greenhouse crops will be discussed in later chapters. It 
should be said here, however, that a uniform tempera- 
ture is important, unless sunshine should cause a wide 
range in temperature, which will do no harm if free venti- 
lation is given. An inadequate heating plant may be 
responsible for low temperatures that are disastrous to 
the crops. Ordinarily, excessively high temperatures 
with poor ventilation do more harm than insufficient heat. 
Ventilation—The necessity of ventilation was dis- 
cussed in Chapter VIII on Diseases and Their Control. 
Every practical grower knows that plants in houses im- 
