438 Pobnaise Method of Heating Greenhouses, ^c. 



If the temperature of the house is kept high, excitability 

 •will remain in a state of continued action, and the plant will 

 be deprived of that rest, which is allotted to it by nature, 

 and, consequently, though it may elongate its shoots, its 

 vital energies will be exhausted and its death will soon fol- 

 low. Instances of this have come under the observation of 

 €very one, where a high night temperature is kept up and 

 the atmosphere saturated with moisture ; the plants will ex- 

 pand their half-organized shoots during the night, but if the 

 sun shines on them the following day, the very rays that 

 should strengthen and consolidate their tissue are too power- 

 ful, even at mid-winter, and in a few minutes they appear 

 as if they had been plunged in boiling water, and ultimately 

 dry up ; this is the effect of excessive moisture and a high 

 temperature. 



But, on the other hand, if the hygrometric state of the at- 

 mosphere be kept high, and the temperature low, the moist- 

 ure is then absorbed by the dormant leaves and branches of 

 the plants, without their being able to decompose it ; these 

 absorbent parts become distended with water and decompo- 

 sition takes place, — or what gardeners technically term damp- 

 ing off. These decomposing portions become covered with 

 a crop of microscopical fungi, and in many cases the decay 

 thus caused is attributed to attacks of insects or something 

 else than the real cause, to which, however, it is very easily 

 traceable, viz., the presence of moisture in excess in the at- 

 mosphere. 



The same effects are produced on fruits in their process 

 of maturation, when the use of artificial heat from drying 

 and absorbing surfaces renders much evaporation necessary. 

 But under such circumstances evaporation should seldom be 

 resorted to, for the injury is more certain than the probable 

 good that will follow. A less humid atmosphere is more ad- 

 vantageous to fruits of all kinds, when the period of their 

 maturity approaches, than in the earlier stages of their 

 growth, and the excess of moisture necessary to restore the 

 aqueous vapor of the atmosphere of a hot-air stove, would 

 prove, — and in our experience has done so, — injurious to 

 forced fruits, and other vegetable productions. 



