; GREENHOUSES 



cases they must be equipped with facilities 

 for artificial heating. 



In a general sense, the term greenhouse re- 

 fers to those glass structures used for the 

 growing of plants. They are for the most 

 part above ground and are house-like in ap- 

 pearance. There is, however, another gener- 

 al class of glass structures also used for the 

 growing of plants but which are low and 

 often almost wholly under ground. Unfor- 

 tunately, there is no general term commonly 

 applied to them as a class, but since it is 

 common to use in their construction certain 

 standard-size glass sash, the author ventures 

 to suggest the term sash-bed as a general 

 one to include structures of this class; and it 

 is so used in this book. 



CLASSES OF SASH-BEDS* 



Hotbeds. These are low structures, being 

 almost wholly under ground, but having a 

 glass roof made up of sash which are of con- 

 venient size to be lifted off, so that the grow- 

 er may care for the plants. They are usually 

 warmed by the heat generated by decaying 

 vegetable matter, commonly horse manure. 



*For details see Chapter II. 



