108 VEGETABLE GARDENING 



The same treatment may also be given the center bench. 

 But where the plan is followed of making up a part of the 

 benches with manure, it is well to have some or all of the 

 roof glazed with movable sash, to facilitate the work of 

 putting in and taking out the manure. The use of stable man- 

 ure to supplement the heating apparatus is a practice that 

 may be economically followed in locations where coal is 

 high priced and stable manure abundant. The heating 

 arrangement could be either steam of hot water with the 

 flow pipes high up near the roof, as shown at A and B and 

 the returns at C and D. 



Methods of Heating. There are practically three 

 methods of heating greenhouses; viz., by smoke flue, by 

 hot water, and by steam. Heating by smoke flue is 

 described under the head of fire hotbeds. It has the merit 

 of being easily and cheaply constructed by anyone having 

 some little ingenuity. Even when made on the best prin- 

 ciples it is probably more wasteful of fuel than a good 

 steam or hot-water apparatus, but where inferior fuel can 

 be cheaply obtained a smoke flue may of ten be used to ad van- 

 tage. 



As for the relative merits of hot-water and steam 

 apparatus for heating, it is probably enough to say that 

 each system has its earnest advocates and that very often 

 there is little advantage in favor of either. Where a very 

 large heating plant must be used, making a night watchman 

 necessary, it is best to plan for steam heating at low pressure. 

 For small greenhouses, perhaps a hot-water plant is best. 

 It costs more to put in the hot-water apparatus, because 

 it requires more radiating -surface, since the pipes are not 

 heated as hot as when steam is used. 



Some exclusive merits are perhaps justly claimed for 

 a combination of hot-water and steam, in which system 



