68 MASSACHUSETTS HORTICULTURAL SOCIETY. 



intended to support. Great care should be observed in the bond- 

 ing of such walls. Undoubtedly the best bond for such purposes 

 is that known as "Old English," which consists of alternate 

 headers and stretchers, the objection to this being that as the 

 dimensions of bricks vary in different localities, many are such as 

 to make it difficult for the mason to prevent several vertical joints 

 coming directly over each other, and thus causing a weakness in 

 the wall. This difficulty can, however, be overcome if a little 

 care is exercised and the mason when finding joints overrunning 

 will cut a brick or two to bring joints into the desired position. 

 The next manner is to make every third course of headers ; this 

 finds prefereuce with most masons, and gives a good, substantial 

 foundation. 



Theoretically, hollow walls are warmer than solid ones, but in 

 practice they are colder and much weaker, and will be found a 

 source of constant trouble and annoyance, unless you are willing 

 to make both sections eight inches thick, which, with the addition 

 of the air space would make a wall twenty inches thick, and besides 

 being very costly, would occupy more space than we should care to 

 devote to such a purpose. 



The difficulty with the hollow wall, as ordinarily constructed, 

 i. e., two four-inch walls with a two or four-inch air-space 

 between, is that the action of the elements on the outer wall, and 

 that of the heat and moisture on the inner wall soon cause the 

 joints to crack, thus allowing a circulation of air to take place 

 between the walls, which destroys the looked-for warmth caused 

 by the nonconductiveness of the dead air space, and the variable 

 strains brought to bear by expansion and contraction, heat and 

 cold, dryness and moisture, on the two four-inch walls are such as 

 soon to break all bond between the bricks ; and unless the two 

 walls are so tied together as to be practically solid, they will 

 bulge and warp, and endanger the entire superstructure. 



I would particularly caution you against the use of a single face 

 of four-inch brick on the outside ; if any particular color or make 

 of brick is desired, for the sake of appearance, make the outer 

 headers, as well as the stretchers of such brick, and see that the 

 inner brick are of the same size as the face, or make the entire 

 wall with the special bricks. No amount of wire or metal ties 

 will take the place of brick bonds in a greenhouse wall. Tliis 

 same caution pertains to the facing of the inside walls with white 

 enameled bricks, which give a very nice and clear effect. If such 



