8 GREENHOUSES 



er, in order to prevent the heat from escaping 

 or the frost from "entering" through the 

 roof. It was not until the early part of the 

 :8th century that glass roofs were found to 

 be practicable, and they were even then slow 

 in coming into use. 



The first greenhouses in this country sug- 

 gestive of the modern forcing house came in- 

 to existence toward the close of the i8th cen- 

 tury. For the most part they were narrow 

 houses of the shed-roof type, having a solid 

 wall to the north and a glass roof sloping to. 

 the south. They were warmed by flues, 

 usually of brick, passing through the entire 

 length of the house, and connected with a 

 brick fireplace at one end and a chimney at 

 the other. Following this, there came in 

 rapid succession, improvements in form and 

 methods of construction and especially in 

 heating, both steam and hot water, being 

 used early in the iQth century. 



The real progress in greenhouse construc- 

 tion in this country came with the industrial 

 development of the country after the Civil 

 War. The United States census reports show 

 that there was but one commercial green- 

 house prior to 1800; only three prior to 1820, 



