36 Diseases of Greenhouse Crops 



Crete walks on either side of the house. By using 

 a pulley, the pan may be conveniently placed 

 wherever desired. 



Perforated Pipe Method. The apparatus consists 

 of a set of perforated pipes buried in the soil and 

 connected with a steam boiler. The main and cross- 

 head pipes are 2 inches and those which are buried 

 lyi inches. The length of the beds, and especially 

 the capacity of the boiler, will determine the num- 

 ber of pipes to use. However, 7 to 8 pipes are as 

 many as could be used to advantage. These should 

 not be over 40 feet long. The perforations should 

 be one-eighth to three-sixteenths of an inch in size, 

 12 to 15 inches apart and on the upper side of the 

 pipes. The latter are buried about six inches deep 

 and when the steam is turned on the beds are cov- 

 ered with a heavy canvas to retain the heat and to 

 prevent the escape of steam (fig. 6, a and b.). When- 

 ever convenient, it is well to have two sets of pipes 

 so as to save time and fuel. 



Steam Rake Method. This consists of a two-inch 

 main pipe which may be run between two sets of 

 houses. The pipe is connected with the boiler at 

 one end and with a heavy hose at the other. The 

 rake is attached to the hose through which the steam 

 is introduced. There are either two rakes used in 

 a single house, or four rakes operated in pairs, end 

 to end in two adjoining houses. The rake is gener- 

 ally composed of three main pipes 13 feet long, 

 which run crossways of the house, and of several 

 cross pieces one inch in diameter that are gradually 



