WATERING, HEATING, VENTILATING AND SHADING 153 
rules can be made relating either to the amount of water 
which should be used or the frequency of its application. 
This operation calls for the exercise of good judgment. 
The plants themselves tell the experienced grower when 
they are in need of water. If they wilt or even appear to 
droop, there is no question about their requirement, un- 
less the heat of the house is excessive and the humidity 
unusually low. The color of the leaves is a valuable 
guide to the right amount of water. Light green foliage, 
if temperatures are normal, indicates the use of too much 
water, while a dark green color shows that this factor is 
being properly regulated. Examination of the soil is also 
valuable in determining when water should be applied. 
Temperature of water.—Much has been said in favor of 
warming the water during the winter, before,it is applied 
to the beds. It is doubtful, however, whether instances 
can be cited in which the use of cold water has actually 
caused serious injury of any kind. Difficulties may arise 
after the use of cold water, but the probabilities are that 
they are due to cloudy weather or other causes rather 
than to cold water. The fact is, if water is applied in a 
fine spray, every globule will take on the temperature of 
the air before it reaches the soil or foliage of the plants. 
In sub-irrigation, where a stream of water is turned into 
the tile, there may be some objection to using cold water, 
but even in this case the water would soon acquire the 
temperature of the soil. However, there is some evidence 
that the use of warm water in sub-irrigation tile is an 
advantage to crops requiring especially warm soils. 
Methods of watering.— Various factors should be taken 
into account in the consideration of different methods of 
watering. Among them may be mentioned: 
(1) Cost of installation. The cost of installing a given 
system may be slight, but if it is unsatisfactory there is 
no justification for its use. ; 
(2) Effect on plant growth. One system may be better 
