CONSTRUCTION 363 



the frame and a six-inch plank for the lower side. The 

 location and general construction is otherwise very similar 

 to that of the hotbed. For some crops, it is desirable to 

 dig a shallow pit in order to provide room for the tops of 

 the plants. For example, to grow tomato plants, it will 

 require a deeper frame than for radishes or lettuce. These 

 frames are easily moved from one place to another and are 

 often used to force plants in the spring that have been 

 previously started in the fall. Their chief function is to 

 grow plants that have been previously started in the green- 

 house or hotbed, and to harden plants that have been 

 grown in the greenhouse, before setting them in the field. 

 The cheapness of their construction makes them extremely 

 desirable. 



Greenhouses. The out-of-season demand for many of the 

 vegetables has resulted in the construction of large green- 

 houses. These have many advantages over hotbeds. 

 The conditions of temperature and moisture can be defi- 

 nitely controlled and crops can be produced during the 

 most unfavorable weather. They provide profitable em- 

 ployment for the market gardener the year round and are 

 also valuable for starting early plants to be later trans- 

 planted to the field. 



In selecting a location, it is desirable to choose a site 

 that is protected from the north and west, that has a good 

 exposure to the south, and that is unshaded by other 

 buildings. 



Construction. --The heat and moisture within a green- 

 house causes rapid decay of wooden parts. Cypress and 

 cedar are the most durable kinds of wood and are there- 

 fore largely used for this purpose. Probably the most 

 practical form of construction is what is known as the semi- 



