74 GARDEN FARMING 



Pure air is as essential to growing plants as it is to animals. The 

 greenhouse should be provided with ventilators which will permit 

 the introduction of air, even during days when the temperature out- 

 side is very low. Confined air gets supercharged with moisture, and 

 the plants soon rob it of its carbonic acid and other elements essen- 

 tial to their growth. Greenhouse ventilators, especially for a large 

 structure, should be arranged not only along the ridge in such a 

 way as to admit air with the least possible draft upon the plants 

 but also at the side, either above or under the benches, near the 

 ground line. Ventilation is absolutely necessary during the early 

 spring months, when the sun temperature begins to increase and 

 before it is desirable to shade the house with whitewash or paint. 



Various devices for lifting the ventilators are in use by florists. 

 There are two prevailing styles of arranging the ventilator sash. 

 One is to place the sash end to end in continuous rows on one or 

 both sides of the ridge, and to hinge them either to the ridge or to 

 the header, according to whether they are to be opened separately 

 or together, as shown in figure 18. Another plan is to use the 

 ventilator sash at intervals, and so to arrange them that they alter- 

 nate with one another on each side of the ridge ; when so arranged 

 they are usually hinged to the ridge. For vegetable forcing in- 

 dividual sash, consisting of about 6 of the panes of glass used in 

 the structure of the roof, placed at intervals of from 4 to 6 sections 

 of glass, will as a rule be found sufficient for the ridge ventilation. 

 For other crops such as carnations, roses, etc. a more liberal system 

 is desirable. 



Construction of the greenhouse. The construction of the green- 

 house may be that of a shed with a long, flat roof exposed to the 

 south, a short, comparatively steep side which is often shingled, 

 and a high board wall which is made as nearly cold proof as pos- 

 sible by double boarding and by the use of paper at the north. 

 This wall is frequently 10 or 12 feet high, with the ridge of the 

 building 2 or 3 feet higher. The flat roof extends from the ridge- 

 pole to within 4 feet of the ground on the low side, as shown in 

 figure 22. A house constructed on this plan may be increased to 

 any desired length, provided steam heat is used. While the shed 

 construction is a common and popular style in some localities, in 

 others the ridge-and-furrow type of structure with posts 7 or 8 feet 



