388 BOARD OF AGRICULTURE. [Pub. Doc. 



the front Avail is obtained by inserting into the plate of 

 ordinary form a " dri}) board" six to eight inches wide, as 

 in Fig. 8. 



Ventilators. — These should be placed a])out the houses 

 in such a way as to give the proper amount of air for the 

 crop grown, and be used for this purpose alone, and not to 

 regulate the temperature. The skilful fireman will so regu- 

 late his fires as to require but little movement of the venti- 

 lator to keep up the even degree of heat re(j[uired. 



For forcing roses and other plants requiring a high tem- 

 perature, and that are easily injured by a draught of cold 

 air, the ventilators should be placed only on the south side, 

 and be hinged so as to open at the top, that the cold air 

 may enter at the highest point and become warm before it 

 comes in contact with the tender plants. For growing 

 plants that succeed at a low temperature, and that require 

 much air, ventilators are often placed on both sides of the 

 roof, at the front and sometimes on the back walls. One 

 advantage of havini): ventilators on all sides of the house is 

 that by opening all a very short distance a large amount of 

 fresh air may be admitted without causing a chill ; but, on 

 the other hand, the more ventilators used in the construction 

 of the house the greater the cost. Side ventilators are dif- 

 ficult to construct and operate, as they must shut into a frame 

 in order to make a close joint, and continued moisture dur- 

 ing the summer and freezing weather in the winter cause 

 them to open with difiiculty, and they are soon wrenched 

 and twisted out of shape. Ventilators on the roof are now 

 constructed with a groove on the under side, which shuts 

 down upon the tongue of the sash bar, as in Fig. 10, thus 

 making a close joint and yet opening easily in all weathers. 

 All sash fittings, like hinges, etc., should be put on with 

 brass screws, as iron screws rust very quickly and soon rot 

 out the Avood through which they are driven. 



Painting. 

 In building greenhouses, all the framework should be 

 [)ainted with a priming coat of thin lead and oil paint before 

 being fitted, and then all joints covered with thick white 



