FORCING AND FORCING STRUCTURES 6 1 



of the pit wall itself. Such hotbeds may be 6 feet wide to carry 

 one line of sash, or 1 2 feet wide to carry a double line, the design 

 in all cases being such as to conform to the standard 3x6 foot 

 sash. Another type of permanent hotbed is constructed to take 

 advantage of steam or hot-water heat from a greenhouse heating 

 plant. Such hotbeds use no fermenting material, are permanent 

 in character, but are brought into requisition only as needed to 

 start plants in the spring. They are used by amateur and pro- 

 fessional gardeners handling greenhouse and bedding plants to a 

 much greater extent than by growers of vegetables. 



Greenhouse construction and management. The modern forcing 

 structure is an immense glass shed provided with steam or hot 

 water pipes to maintain the desired temperature, and with as light a 

 framework as will carry the amount of glass necessary. The objects 

 to be attained in such structures are: (i) light; (2) a proper de- 

 gree of heat ; (3) sufficient ventilation ; (4) a certain degree of per- 

 manency ; and (5) sufficient water facilities for maintaining the 

 proper humidity. 



To secure the maximum amount of light in a forcing structure, 

 it is necessary to dispense with as much timber as possible in the 

 framework of the building. To this end, modern greenhouse con- 

 struction has reduced itself to the use of small rabbeted strips of 

 wood, usually ij- or 2 inches deep by i^ or i J inches thick, and if 

 possible cut the length of the slope of the roof. These strips, which 

 are technically known to greenhouse builders as sash bars, are 

 rabbeted, as shown in cross section in figure 18, A, so as to carry the 

 glass, and are placed the proper distance apart to receive glass of 

 the desired width. The weight of the structure is lessened and the 

 light-obscuring features are decreased by the use of gas pipes for sup- 

 porting posts, as well as for purlins and trusses (see figure 18, J3, B\ 

 The amount of light may also be increased by the use of wide 

 or large-sized glass, which, of course, requires fewer sash bars 

 and consequently results in less shading from the framework of 

 the building. A popular size of glass is 16 x 24 inches, while 

 many growers use an even larger size. Some put the glass in the 

 24-inch way, thus placing the sash bars 24 inches apart. The 

 writer's personal preference, however, is for sash bars spaced to 

 carry 1 6-inch glass, which makes a somewhat stronger roof than 



