Jan.] 



GREEN-IIOUSE AND CONSERVATORY. 



1005 



VENTILATING. 



The admission of fresh air is an indispensable part of good 

 culture, for, without it, the plants would soon be drawn up 

 and naked, and many of tlicm lose their leaves, and even die, 

 while the more hardy would become weak, and naked at their 

 bottoms, and devoid of colour. Where plants stand crowded 

 upon stages, a circumstance not easily avoided when the cul- 

 tivator is ambitious of the number or richness of his collection, 

 or when, from a similar cause, they are planted too crowded 

 in the borders of conservatories, air in such cases should be 

 particularly attended to. In this respect, those houses which 

 are capable of being partially removed, become of the greatest 

 use ; but all houses for the cultivation of these plants should, 

 in their first erection, be made capable of being completely 

 ventilated, so that three parts of the year the plants may en- 

 joy nearly as much fresh air as if they were planted out. 

 During this month, care must be taken that this element be 

 as abundantly supplied as possible, for which purpose, the 

 ventilators should be opened both at the back and front ; and, 

 in mild days, some of the sashes should also be partially opened 

 for a few hours. However, in times of cutting frosty winds, 

 a sufficiency of air will find its way into the most completely 

 finished houses through the spaces between the laps of the glass, 

 and at other crevices, to render the opening of the ventilators 

 unnecessary. Air may be safely admitted at this season to kec^p 

 the thermometer as low as 40° during the time of its admis- 

 sion. It may be here also remarked, that it is not altogether 

 in the size of the spaces opened, nor the length of time that 

 they remain open, that changes the air most completely in any 

 structure. The difference of its specific gravity should be 

 taken into consideration, and as that which is colder is con- 

 siderably heavier than that which is hotter, and as it has been 

 sufficiently demonstrated that the lightest or warmest air accu- 

 mulates at the top of the house, it therefore follows, that when 

 the top ventilators or the top part of the roof is opened only, 

 the heated air will ascend by the force of its own gravity, un- 

 assisted by any other impetus ; whereas, if the bottom ven- 

 tilators or lower part of the house be opened only a small 



