296 



VENTILATION. 



looked, because it has not been so clearly- 

 understood by those who build houses 

 for plants, as by those who grow plants 

 in them. Almost all the great plant 

 structures with which I am acquainted 

 are notoriously deficient in this respect. 

 Plate-glass and metallic sash-bars offer 

 little obstruction to the admission of light 

 and heat transmitted from the sun ; and 

 on this account, anomalous as it may ap- 

 pear, their value in horticulture is esti- 

 mated ; and so it should be, because the 

 watery juices of plants are elaborated just 

 in proportion to the presence of them ; 

 but then they should be present natu- 

 rally and relatively." 



Much of the want of success in grow- 

 ing plants in large houses, the intelligent 

 authority above quoted attributes to the 

 great difference of temperature between 

 the soil in which they are planted and 

 the air in which they breathe — the want 

 of heat in the former, and the excess of it 

 in the latter. 



" It is an easy matter to design elegant- 

 looking hothouses and conservatories, and 

 of any conceivable dimensions ; but it 

 most assuredly does not follow that their 

 usefulness depends upon their architec- 

 tural proportions or embellishments, or 

 on the number of roods or acres they 

 may cover. The contrary is always the 

 case, because the larger the house, so in 

 proportion does ventilation become of 

 greater consequence ; in fact, its necessity 

 and importance are exclusively governed 

 by this circumstance. The ventilation 

 afforded to small houses is generally suffi- 

 cient, as the space enclosed is so small, 

 and the movable sashes so numerous, that 

 complete command is obtained over the 

 temperature ; not so, however, in those 

 immense glass balloons, or rather, as 

 they may be well termed, mausoleums in 

 horticulture, as their occupants commonly 

 show them to be." 



The following diagram, fig. 399, will 

 show sufficient and insufficient ventila- 

 tion as relates to large houses. " Take, 

 for example," says Mr Glendinning, "a 

 conservatory similar to that represented 

 by the woodcut, and only imagine the 

 sashes a a to open, with small ventilators 

 in the wall at d d, and with a clear sum- 

 mer sun striking fervidly upon it. The 

 heat in a house of this kind, it will be 

 readily admitted, would be quite insuf- 



ferable ; neither animal nor vegetable life 

 could long withstand it. Now, if provi- 

 sion had been made in this conservatory 



Fig. 399. 



for the sashes to open at b b and c c, which 

 undoubtedly ought to have been the case, 

 the temperature would instantly and 

 easily be reduced to any desirable extent 

 consistent with the kind of culture in 

 progress." 



The theory of artificial motion being 

 communicated to the atmosphere and 

 plants in large houses, has been advocated 

 by Knight, Dr Lindley, and various writers 

 on vegetable physiology and pathology ; 

 and to effect this has been the study of 

 several horticultural architects, Mr Glen- 

 dinning amongst the number. We shall 

 not stop to inquire into this theory at 

 present, satisfied as we are that the means 

 employed to produce that effect will be 

 exceedingly favourable to the production 

 of ample ventilation. " The interchange 

 of atmosphere constantly going on" to 

 effect this, " and the motion in which it 

 is continually kept," says Mr Glendinning, 

 " from being thus circumstanced, is a to- 

 lerably clear proof of the immediate cause 

 of the healthiness of plants in" small 

 " houses j and there is one other reason, 

 also equally clear, that the inequality of 

 temperature in such buildings is mani- 

 festly inconsiderable compared with build- 

 ings of large dimensions. In houses con- 

 structed like that which the accompanying 

 woodcut represents, fig. 400, the pipes are 

 usually carried immediately round the 

 inside of the front wall. The heat, there- 

 fore, passes up under the glass, until it 

 reaches the highest part of the building — 

 that part generally being intolerably hot. 

 The great body of air in the centre of the 

 house remains stationary, and does not 



