314 FORCING GARDEN. 



situdes of our climate. For the sake of convenience, 

 we shall adopt the term in its broadest acceptation. 

 After some preliminary observations, we shall first treat 

 of the structures, and then of the fruits and vegetables 

 which are cultivated in them. 



The principal object of hot-houses, and other struc- 

 tures of a similar nature, is to produce an artificial 

 temperature and humidity of the atmosphere, which 

 shall resemble, as nearly as possible., the climate in 

 which the fruits or plants naturally flourish. A com- 

 mand of heat is obviously a primary requisite. A re- 

 gulated admission of air, and the presence of a certain 

 degree of moisture, are, in the next place, necessary. 

 Lastly, without the free access of light, plants become 

 blanched, or are destroyed by the moisture which they 

 generate. These, then, are the conditions which limit 

 the form of hot-houses ; when these are attained, any 

 form may be adopted which invention can devise, or 

 wealth execute ; but every true lover of the art will 

 aim at simplicity, and will deprecate useless expendi- 

 ture, so often exhibited in this department, as injurious 

 to the character as well as to the progress of horticul- 

 ture. 



Artificial Heat. — Forcing-houses are heated in various 

 ways ; by means o^ flues conveying smoke and heated 

 air ; by 'pipes conducting steam or hot water; by so 

 constructing the glazed house as to increase the calo- 

 rific action of the sun's rays ; and sometimes by the 

 heat generated in the course of the fermentation of ve- 

 getable substances. 



Flues are generally constructed of common brick, 

 though occasionally fire-brick is employed in the nech^ 

 or that part of the flue immediately adjoining the fur- 



