26 DISEASES OF GLASSHOUSE PLANTS 
‘“‘ damping off ”’ of tomatoes, and also “‘ canker ” of the 
cucumber and melon. Surface watering by means of 
hoses is almost universally adopted by the practical 
man, and ingenious methods have been devised to 
regulate the rate of distribution. 
In this country overhead watering is still in its infancy, 
but it possesses the advantage of uniform distribution. 
A dry atmosphere can be moistened quickly, which is 
an advantage during hot summer days, but a disad- 
vantage in dull weather, as the excessive moisture on 
the leaves encourages disease. Also, because it is purely 
mechanical, it does not cater for the special needs of 
individual plants. 
The use of perforated hoses, laid on the ground in such 
a manner that the issuing jets make impact with the 
soil midway between the plants, has lately been adopted 
and has proved an efficient and labour-saving device. 
Sub-irrigation has not so far found favour with the 
practical man, but experimentally it has proved 
extremely successful. The absence of surface moisture 
prevents the rapid spread of fungus parasites, and 
consequently diseases such as “damping off” and 
** foot rot ”’ are avoided. 
Mulching 
The process of mulching, so familiar to nurserymen, 
fulfils the dual purpose of conserving the soil moisture 
and providing a top-dressing of plant foods. While it 
is recognized that on some lands mulching is a necessary 
adjunct to the growing of profitable crops, the view is 
gaining favour that on other lands the cost of this practice 
is out of all proportion to the effect produced. 
During the years of war stable manure was difficult 
to obtain, and where procurable was obtained at a high 
cost. In the tomato industry, where mulch is applied 
at the rate of 20 to 25 tons per acre, these conditions 
induced some nurserymen to refrain from mulching their 
