No. 4.] GREENHOUSES. 383 



may be attached to the south side of a stable or dwelling- 

 house, and, being sheltered from the north, requires only 

 comparatively little heat, but, on the other hand, cannot be 

 as well ventilated as a house exposed on all sides. 



The three-quarters-span house (Fig. 2), facing the south, 

 is the one most used by commercial florists and market 

 gardeners. It possesses the advantage of being cheap in 

 construction, affording the greatest amount of sunshine, and 

 may be ventilated from all sides when necessary, for grow- 

 ing crops require low temperature and an abundance of 

 light. 



The foundation of these houses may be of stone or 

 cement, or the walls may be built upon chestnut posts set 

 deep in the ground, or cast-iron posts made for this purpose. 

 The north wall is made of non-conducting material, while 

 the south wall is of glass. 



The even-span house (Fig. 3) is generally placed north 

 and south, and has the advantage of exposing the plants to 

 sunlight upon all sides, and receiving the greatest amount 

 of sun's heat and light in the morning and afternoon. This 

 is much used for the growth of roses, chrysanthemums, etc. 



The side-hill house (Fig. 4) possesses some advantages 

 over those already mentioned. When built on a south, 

 south-east or south-west slope, they are perfectly protected 

 on the north, and susceptible of perfect drainage, no matter 

 what the nature of the soil. The cost of the side walls and 

 the terrace walls (Fig. 4, a) is much less than that of out- 

 side walls and beds or benches in the other forms of houses. 

 It is practically a one-roofed house with no gutters. One 

 objection to this form may be found in the effort required 

 in going up and down from one part of the house to the 

 other. 



Materials. 



The best wood for greenhouses is cypress or clear-heart 

 white pine, the former being generally considered the best, 

 because of its straisfht o-rain and the great length, but it is 

 more liable to warp out of place unless firmly nailed when 

 put in place. 



