CONSTRUCTION AND HEATING OF GLASS HOUSES. 75 



To a question as to best size of glass, Mr. Gibbons answered 

 that, as a rule, the glass should be sixteen by twenty-four inches. 



In reply to a question as to the object of grooves in sash-bars, Mr. 

 Gibbons held that the grooves would receive the greater portion of 

 water that was thrown or condensed upon the glass, and convey it 

 to a point over the space between the back of the side benches, 

 and the plate, where the lower side of the groove is cut away, and 

 the water falls directly to the ground. Accumulation of dust in 

 these grooves rareh' amounts to an obstruction. 



It was asked whether it is better to use four-inch or two-inch 

 pipe for heating a greenhouse, and Mr. Gibbons replied that he 

 prefers four-inch to two-inch pipe, although, other things being 

 equal, the effects of both on plant life are the same. But the 

 four-inch pipe is more reliable, having a larger reserve of heat for 

 an emergency, and will last much longer than any smaller, 

 wrought iron pipe. 



Another question was asked as to comparative advantages of 

 the upward and the downward systems of hot-water circulation in 

 greenhouses. 



Mr. Gibbons replied that formerly greenhouses were built to 

 accommodate the heating S3^stem ; but, as in these days we have 

 often to accommodate the heating system to the greenhouses, he 

 thought that under ordinary^ circumstances the system best 

 adapted to the location, grade, and arrangement of the greenhouse 

 would perhaps serve the purpose better than the other. But 

 where the range to be heated includes more than one house, the 

 drop circulation is difficult to manage ; therefore, as stated in the 

 paper read today, taking all things into account, he would 

 strongly advise the upward circulation system in all cases except 

 where the local conditions are such as to render the downward 

 system necessary. 



A question being asked as to comparative advantages of tiles or 

 slate for the bottoms or floors of plant benches or stages, Mr. 

 Gibbons said that tiles are in great favor for bench bottoms ; they 

 are much superior to slate when the bench is filled with soil in 

 which plants are set, but, for plants in pots slate bottoms are 

 preferable. The advantage of tiles lies in the fact that when they 

 are made, a quantity of coarse sawdust is mixed with the sand 

 and clay, and when they are fired the sawdust is burned out, 

 leaving the tile verv porous, thus securing perfect drainage and 

 ventilation. 



