364 ITs'DEX. 



Construction of hot walls. — Figure and description of hot wall. — Varions 

 methods of building hot walls. — Trial of hot walls, covered and uncovered. — 

 Foreign grapes may be grown on hot walls. — Grapes produced on hot walls in 

 England, 210 



New method of propelling heated air liv means of machinery — described ty 

 Mr. Marnock in Gardeners' Journal. — The air propelled by means of a fan, 246 



PART III. -VENTILATION. 



SECTION I. 



PRINCIPLES OF VENTILATION. 



Attention required from gardeners, &c. — Its practical importance. — Power 

 of plants to withstand the changes of climate. — Power of vitality possessed 

 by seeds. — Power of plants to bear high temperatures. — Of bearing delete- 

 rious gases. — Effect of winter-forcing on the odor of flowers — and on the 

 flavor of fruits, 248 



Whether vegetation purifies the air. — Opinions of Priestley — of Dr. Dau- 

 beny, of Oxford — of Dr. Lindley, of llonaon. — Natural adjustment of the 

 atmospherical elements. — Atmosphere of cities. — Benefits of large trees in 

 the streets. — New Haven, the effect of trees in it, 252 



Power of plants to absorb carbonic acid. — Gottingen springs. — Property of 

 charcoal for absorbing gases. — Table of gases and the quantities absorbed by 

 charcoal, • 254 



Power of plants to withstand the vicissitudes of temperature. — Theories of 

 physiologists. — Dalton's chemical philosophy. — His theory of the relations of 

 the atmosphere to heat. — The properties possessed by caloric, 256 



SECTION II. 



EFFECTS OF VENTILATION. 



Effects of admitting cold air into a hot-house. — Moisture carried away, — 

 Necessity of keeping the ffoors damp. — Plants unlike animals in respect to 

 ventilation. — Ventilation not necessary as regards respiration. — Air-tight 

 glass cases for plants, • ' * * ^^^ 



Knight's experiments on grape vines. — The philosophy of this system. — 

 Evaporation of moisture on the glass. — Contaminating gases in the atmos- 

 phere. — Experiments of Drs. Turner and Christison, . .264 



The abstraction of moisture in proportion to the rajtidity of the motion of the 

 air. — Methods of counteracting this loss. — Thermometric changes not sat- 

 isfactory rules for the admission of air, ; • • ^^^ 



Ouantity of moisture contained in the air. — Its capacity for moisture. — 

 Estimated quantity of air escaped. — Estimated quantity of moisture escaping 

 in the air.- - Lofty plant-houses. — Difliculty of managing the atmosphere in 

 them, ' 269 



SECTION III. 

 METHODS OF VENTILATION. 



Improvements af the present methods of ventilation. — Plans adopted \o 

 modity the influence of draughts. — Motion in the atmosphere. — Machinery 

 employed for this purpose. — Detection of currents by a common candle. — 

 Propriety of a rauid mntinn disuuled, 273 



