Vegetables with Edible Leaves or Stems 117 



Sub-irrigation by the use of drain tiles, or other more or 

 less solid pipes laid into the soil, is the better plan. This is 

 especially advisable when the water supply is large and 

 can be cheaply obtained. To make sub-irrigation a suc- 

 cess, it is necessary that the field should have a more or less 

 impervious substratum not more than 5 to 10 feet down, 

 or that the water-table should stand rather near the 

 surface. In this, as in the open ditches, there is a water- 

 main, running from which are the arms that supply the 

 crop. When the land is perfectly level, the lines of tile 

 are laid at regular intervals of 12 to 60 feet. When the 

 land is not level, they must be laid on the contour lines. 

 This is less convenient, since the celery rows must be made 

 parallel to the lines of tile. With a sub-irrigation system, 

 much damage may be done by too free use of water; 

 otherwise it is ideal. In Florida, artesian or flowing wells 

 form a cheap and continuous source of water for irrigating 

 celery. (See lower figure, Plate I.) 



The over-head system of irrigation has been used success- 

 fully with celery in a number of places. Its main difficulty 

 lies in the fact that it brings about conditions favorable to 

 the propagation of leaf blights. In this system the water 

 is supplied as a spray from small nozzles in over-head 

 lines of pipe. 



There is an extensive market for high-grade celery in 

 the late winter and spring ; that is, after the crop grown in 

 temperate climates has become exhausted and before a new 

 crop can be produced. The celery must be crisp and have 

 a nutty flavor to sell well. With rapid and certain trans- 

 portation, celery can be grown in many subtropical 

 regions to supply the large centers of population. 



