HEATH-HOUSES. 



403 



to have the roof portable — that is, com- 

 posed of rafters and sashes — so that part, 

 or all of them, may be removed during 

 summer, to admit of soft genial rains and 

 dews falling directly upon the plants ; — 

 cold and heavy continued rains should, 

 however, be excluded by replacing the roof 

 sashes. The temperature also will be 

 lowered by this means, as the conduction 

 of heat by the glass will be avoided ; and, 

 to break the full force of the meridian 

 sun, thin canvass awnings should be used, 

 mounted on rollers at the ridge, and 

 ready at all times to let down upon the 

 rafters. The side or upright lights should 

 also be made to open freely, and so con- 

 structed as to be capable of removal during 

 summer. All this may be considered ven- 

 tilation enough, — and so it is during sum- 

 mer ; but during winter, when the side 

 lights cannot be opened with safety, on 

 account of the cutting draughts of wind, 

 other and more judicious means must be 

 employed ; and no plan is so simple, and 

 at the same time so effectual, as ventila- 

 tors in the side walls opening into the 

 house close to the floor, by which atmo- 

 spheric air, fully charged with moisture, 

 will enter, and, becoming diffused through 

 the house and amongst the plants, will 

 find an escape through the openings in 

 the ridge-board, as shown in several 

 figures in section Ventilation. The air 

 thus admitted does not come into contact 

 with the plants, but enters below them, 

 and, ascending upwards, parts with its 

 cold, and imbibes the temperature of 

 the internal atmosphere nearly, before 

 it reaches a single branch or leaf. In 

 the coldest weather this operation goes 

 on, as, when the atmospheric air is too 

 cold to be admitted into the house, it 

 indicates that the hot-water pipes should 

 be put in operation. And, as all kinds of 

 heating should be placed along the sides of 

 such houses, it follows that the cold air, 

 in entering as above, will have to pass 

 under and over the hot pipes or flues, 

 and thus abstract sufficient heat from 

 them to render it fit for being admitted 

 amongst the plants. 



Again, a constant stream of air should 

 be kept going on, we would almost say 

 night as well as day, to counteract the 

 effects of damp, or rather the effects 

 of those gases formed in air in a stagnant 

 and damp state, which are found to gene- 



rate on the floor and near the bottom of 

 all hothouses not sufficiently ventilated, 

 at or under the floor level ; and few 

 houses are exempt from this defect. A 

 rapid circulation of air is absolutely ne- 

 cessary to the welfare of heaths; and this 

 circulation, to be beneficial to the fullest 

 extent, must be frequently charged with 

 moisture, but not uniformly so. Who- 

 ever has studied the habitats of our 

 mountain heaths, or had the good fortune 

 to see this genus luxuriating in all the 

 pride of exotic splendour on the Table 

 Mountain at the Cape of Good Hope, 

 must have experienced the buoyancy of 

 the rarefied air they breathe, the sweep- 

 ing currents of wind, the drizzling showers, 

 the misty dews, and, at times, the low 

 temperature they are exposed to. 



To imitate all these conditions artifi- 

 cially should be our endeavour. This is 

 to be effected by judicious and ample 

 ventilation, and by placing the plants 

 upon open stages, so that the air may cir- 

 culate freely around them, and not upon 

 close stages or platforms, as is too usually 

 done ; by keeping the temperature low, 

 and the atmosphere humid, during sum- 

 mer ; by placing evaporating pans in vari- 

 ous parts of the house, or by watering 

 the floor copiously, particularly in 

 warm weather ; and by currents of air 

 let in on all sides when a drier atmo- 

 sphere may be deemed expedient. 



A complete heath-house should be fur- 

 nished with hot-water pipes of 3 inches 

 bore — that being found sufficient to ex- 

 clude frost, the utmost degree of artificial 

 temperature required. Indeed, where 

 arrangements can be made to exclude 

 frost by neat and portable coverings, it 

 is better to use them, as the heath is, of all 

 other plants, the most impatient of fire heat. 



The accompanying section, fig. 552, 



Fig. 552. 



and plan, fig. 553, represent what we 



