90 MAINE AGRICULTURAL EXPERIMENT STATION. 



should of course be selected with care and cedar or locust 

 should be used. 



Brick and tile are sometimes used for green house walls. 

 There is always danger, however, that because of excessive 

 moisture and frequent changes in temperature such a wall will 

 not prove durable. The brick wall which appeals to me most 

 strongly is one used by Professor Green of Minnesota.* This 

 consists of a four-inch brick wall on each side of a three-inch 

 hollow tile with a one-inch air space on each side of the tile — 

 thus making a thirteen-inch wall. In- this wall we have three 

 separate dead-air spaces, an arrangement from which we should 

 expect excellent results. Such walls, are, however, very expen- 

 sive and not advised for ordinary commercial purposes. 



Some of the houses at the Experiment Station have been built 

 with a double brick wall with an intervening air-space of about 

 two inches. This arrangement is fairly satisfactory provided the 

 brick used are well burned. In any case it is important that 

 the two courses be tied together at frequent intervals. 



b. Roofs: — As already indicated, the simplest form of green 

 house roof is made by the use of ordinary hot bed sash. This 

 form has been modified to a certain extent in the building of 

 orchard houses and other like structures with temporary roofs. 

 In such cases a permanent wooden or iron frame is constructed 

 and sash are put in place whenever the houses are desired for 

 use. At the present time, however, some form of per- 

 manent sash bar is considered preferable. Sometimes rafters 

 of 2x4 stuff are placed about six or seven feet apart to give 

 rigidity to the roof, but the tendency at the present time is to use 

 rather heavy sash bars and omit the rafters. In this climate, 

 because of the excessive falls of snow to which we are liable, 

 sash bars about 2x2 1-2 inches should be used. Purlins should 

 also be placed at frequent intervals. All supports may best 

 be made of gas pipe or small steam pipe rather than of wood. 

 The object in all of the details of construction should be to 

 shut out as little light as possible. The gas pipe puriins may 

 be made to serve the double purpose of supporting the roof and 

 of carrying the water where desired. This method is followed 

 in some of the larger commercial establishments. It has been 



* Bulletin 7, Minnesota Experiment Station. 



