GLASS STRUCTUEES AND APPLIANCES. 



99 



vapour when it was least wanted. This system of 

 having a small offset pipe specially for warming 

 tanks of water is by no means confined to Orchid- 

 houses, but is often used for plant-stoves and fruit- 

 forcing houses, such as Pineries, Vineries, or early 

 Peach or other forcing houses. 



Structural Peculiarities of Plant-stoves 

 and Orchid-houses. — These, unless erected 

 for very tall tropical plants or shrubs, Palms, 

 Ferns, or large flowering or foliage plants, are 

 mostly built rather lower, and constructed with 

 greater care and closeness, than conservatories or 

 Orangeries. And this on the ground of economy, 

 as well as for cultural reasons. Chinks in the glass, 

 indifferently fitting lights, ventilators, or doors, are 

 matters of little moment where the temperature 

 is comparatively low. But where a temperature 

 of fifty, sixty, or more of artificial heat has to 

 be kept up against all the antagonism of wind 

 and weather, a close fit between the internal and 

 external aii* becomes indispensable. The loss of 

 heat through bad glazing, or bad fits, is in- 

 calculable. That loss rises in magnitude and im- 

 portance as the disparity between the internal and 

 external temperature increases. 



Nor only this, but the loss of heat is intensified, 

 and the injury inflicted by the free admission 

 of cold air, or emission of warm air, is increased, 

 in the ratio of the moisture in the internal air. 

 The capacity of air to caiTy vapour is in pro- 

 portion to its temperature. The colder the air the 

 less moist, and vice versa. Hence, as cold air rushes 

 into a plant-stove, or Orchid-house, it commits a 

 two-fold robbery abreast. It steals caloric and 

 aqueous vapour from the air, and if it cannot 

 find enough to satisfy its craving necessities for 

 moisture in the air, it steals it, as we have already 

 seen, from the leaves and flowers of the plants. But 

 as considerable heat was first of all expended in the 

 conversion of water into vapour, it follows that 

 a compound waste of caloric takes place in the 

 escape of heated air into the owtside atmosphere, and 

 the ingTcss of the external air into tropical plant 

 houses. Besides, the evaporation of water from 

 heated surfaces to satisfy the wants of dry cold air 

 for moistiu'e, cools or chills these surfaces, and is 

 thus a source of local evils as well as of a general 

 depression of temperature throughout the entire area 

 of hot-houses. 



These principles have an important bearing on 

 ventilation, as we shall see, for the elfect of cold air 

 on local atmosphere is the same whether the air be 

 admitted through imperfections of structure, or of 

 express purpose through wilfully opened apertures, 

 called ventilators. Though it is needful to pro^dde 



all plant structures with such appliances for the 

 purpose of moderating their heat and renewing their 

 atmosphere, yet the tendency of the latest discoveries 

 in science, and of the more advanced practice, both 

 run in the direction of using ventilators much 

 more seldom and to a lesser extent than formerly. 

 At one time no end of energy, time, money, and 

 appliances were expended in the heating of plant- 

 stoves to the necessary temperature, and the sweeping 

 of the heated air out again through open ventilators, 

 to the injury of the plants, and the reckless waste of 

 heat and aqueous vapour. In regard to the ven- 

 tilation of all tropical plant houses it may be 

 well to be furnished with the power of a giant, but 

 very unwise to use it with a giant's might. The old 

 dogma about the exhaustion of the air through the 

 economy of plant-life is now very generally ex- 

 ploded. The idea seemed to prevail that the same air 

 could only be used once, as water through a watering- 

 pot, or corn through a sieve. But plants use air 

 many times without abusing it — that is, exhausting 

 it — if, indeed, they can exhaust it ; and hence the 

 importance of treating air once heated and charged 

 with moisture as a force to be used many times, 

 utilised to the uttermost, and not simply used 

 once, and swept out at open doors or windows — that 

 is, ventilators. Moist air is the product of many 

 forces, the result of many energies — such, for ex- 

 ample, as perfectly constituted houses, coal, labour, 

 water — all of which cost time and money, and hence 

 ought to be utilised to the very uttermost. 



Height. — It may be needful at times to have 

 lofty and what are called semi-architectural houses 

 for some plants, for effect. But so far as successful 

 culture is concerned, such are by no means needful. 

 In fact, and in practice, size and height of house 

 are rather unfavourable to culture than otherwise. 

 Large and lofty houses are mostly cold, and the 

 coldness arises very much from their size and their 

 loftiness. Of course any sized house may be heated 

 if a sufiiciency of furnace and boiler area and hot- 

 water pipes are used. But even then such houses 

 seldom equal the cultural results obtained in lower 

 and smaller houses. Fortunately, too, houses may 

 be large without being lofty, and larger cultural 

 areas be enclosed at less cost within from six to ten 

 feet of the ground than sixty. Nor does the effort 

 after low houses end on the surface. A great many 

 plant-stoves and Orchid-houses are sunk several feet 

 below it. The system is most economical as well 

 as favourable to culture ; for all the underground 

 portions of such houses are impervious to any 

 amount of cold in the atmosphere. Such houses 

 are virtually glass roofs spanning the walls. Not 

 unfrequently the front wall is buried right up to the 



