156 GREENHOUSES 



wide. In commercial houses with high 

 benches, from 20 to 24 inches is a common 

 width. When low beds are used, the walks 

 are sometimes as narrow as 14 or 16 inches. 

 It is often advisable to arrange the 

 benches so as to have the center walk of ex- 

 tra width, which will allow of the use of 

 a wheel barrow or .cart in removing and re- 

 plenishing the soil and for other purposes. 



Material for Walks. Concrete is unques- 

 tionably the best material for walks. Water 

 has no effect on it; it is substantial; it may 

 be used as a foundation on which bench legs 

 and ventilator columns may stand; and it 

 may be quickly and easily laid. In conserv- 

 atories and private houses nothing can take 

 its place. For data on concrete construction 

 see Chapter XIV. 



In commercial houses coal ashes are often 

 used. Ashes must be kept away from the 

 pipes as the sulphur they contain will cause 

 the pipes to corrode very rapidly. 



Curbs. For convenience and cleanliness, 

 many growers who plant directly on the 

 ground prefer to have their houses marked 

 off into regular beds, divided by narrow 

 walks and surrounded by a curb to keep the 



