96 MASSACHUSETTS HORTICULTURAL SOCIETY. 



but when heated by the suu, the difference was increased to three 

 or four degrees. In this case the circulation of the warmed air 

 was perfect, as was shown by the slight motion of foliage at 

 various elevations. 



In another large conservatory, which was heated in part over- 

 head, the ditference in temperature at the floor from that at the 

 ridge was ten degrees or more, and there was no perceptible 

 circulation of the air. 



In the lofty building there were no pipes in the centre, but in 

 the latter house there were central pipes, and the air was, in effect, 

 bottled up or stationary. Still air is the best non-conductor. The 

 lecturer said that he would never put any heating apparatus in 

 the ridge of a building. By having ventilators at the ridge, and 

 side ventilators at the plates, the extra sun-heat is carried up the 

 glass roof without penetrating the centre of the house or coming 

 in contact with the plants, and the admission of cold air at the 

 sides will force out extra heated air at the top, and carry out gas 

 also. But watchful care is necessary to prevent any strong drafts 

 through the interior of the greenhouse, which every florist will 

 agree is very objectionable. An English gardener, on first 

 observing this system, objected to it quite strongly ; but after a 

 few mouths' experience and observation he declared that this 

 house was the best ventilated of any he was ever in. 



There is a tendency among florists to dispense with side ventila- 

 tion to a large extent. They seem to consider two continuous 

 lines of ventilators along the ridge, one each side, to be the best ; 

 that if opened on the north side when the wind is southerly, and 

 opened upon the south side when the wind is northerly, they have 

 the perfection of ventilation. We should bear in mind that much 

 ventilation is given by unavoidable openings, as greenhouses are 

 rarely tight. 



As to the aspect of the greenhouse, a three-quarter-span roof 

 extending nearly east and west, facing south, would be the best 

 for rose houses. If this house be turned round and the glass is 

 run down to the level of the bed, we have the modern, short south- 

 roof plan. In an ordinary three-quarter-span house, by bringing 

 up the benches, plants can be grown uniformly near the glass. 



In a range of adjoining houses there is no opportunity to let in 

 air at the sides. If your liouse is twenty feet high the plants will 

 be from fifteen to eighteen feet from the glass. 



