WATERING, HEATING, VENTILATING AND SHADING 155 
and the crop is being harvested. Ordinarily, it is prefer- 
able to apply water in a fine spray or mist, and this is not 
possible without the use of a special nozzle which may be 
attached to the hose. Fig. 52 shows a most serviceable 
nozzle for the watering of small plants, and it is also con- 
venient for watering limited areas here and there which 
may need water before the time of the next general water- 
ing. Some form of hose’ watering is used more or less in 
all commercial establishments. A combination of two 
systems is ideal. For example, sub-irrigation is highly 
satisfactory for lettuce, but many growers prefer the hose 
or perhaps the overhead system for cucumbers, partly be- 
cause they are valuable in controlling the red spider. 
The hose and overhead watering also make a desirable 
combination. Though the expense of installing two sys- 
tems of watering may seem excessive, the advantages 
thereof may more than justify the additional expenditure. 
Watering with a hose, unless carefully managed, may 
result in the incrustation of the surface of the soil. To 
avoid this difficulty, the spray should be as fine as 
possible and the hose should not be held too long at one 
place. 
Sub-irrigation—Several agricultural experiment sta- 
tions have conducted experiments in the watering of 
greenhouse vegetable crops by means of sub-irrigation. 
The work of the Ohio station has attracted most atten- 
tion. In the institutions where sub-watering has been 
tried, the results have generally been favorable to this 
system. For reasons, however, which cannot be satis- 
factorily explained, sub-irrigation has not become popular 
among commercial greenhouse men. A grower here and 
there is using the system, but the rank and file of the 
gardeners who produce crops under glass have not 
adopted this plan of watering. It is presumably due to 
the cost of installation. There is also some objection to 
having the tile in the beds where they interfere more or 
