82 THE NEW KHUBARB CULTURE. 



under greenhouse benches is described in Part First. 

 Chapter II. 



One grower near Boston estimates the yield of rhu- 

 barb under glass at 20 pounds per sash, worth at five 

 cents per pound, $1. The distance here was 2x2 feet. 

 The crop grew in about five weeks, after which the glass 

 was removed and used over radish hotbeds. Steam was 

 used to force this crop, the roots remaining in the ground 

 throughout the year. 



Steam Forcing in Open Fields. — Winter forcing in 

 the open field has been found practicable, the soil being 

 heated with steam or hot water introduced through 

 underground tunnels. European gardeners sometimes 

 construct permanent tunnels of brick between the rows, 

 and heat the plant beds with hot water through pipes 

 laid in these tunnels. A less expensive plan of field 

 forcing has been successfully tried at the Missouri ex- 

 periment station; asparagus being growm from 1896 to 

 1899, while during the season of 1900-1901, the rhubarb 

 crop was treated in precisely the same manner and with 

 every indication that the results would be equally favor- 

 able. 



The idea of this method is to avoid the expense of 

 piping or other construction, l)y blowing hot steam into 

 board tunnels betAveen the rov/s. Trenches were first 

 made between the rows, which are four feet apart. They 

 were opened with a plow, going once through and back 

 again, and were made uniform by means of a spade. 

 These trenches were then covered with 12-inch boards, 

 which rested on four inch blocks, placed at frequent in- 

 tervals along either side of tlie trenches. This formed 

 tunnels between the rows for conducting the steam. To 

 guard against the steam's escaping, two or three inches 

 of soil was placed over the boards, and the plot was then 



