STRUCTURAL 13 



greenhouse. It may be built with any aspect from 

 south to west, and for certain purposes, such as the 

 cultivation of Ferns, a house of this form facing north 

 is most useful. The worst aspect of all is towards the 

 east. 



The internal arrangements should consist of a narrow 

 front stage, then the path, leaving the biggest space for 

 the back stage. This latter may be built in tiers like a 

 series of steps if the height of the roof permit, and 

 will then present more staging room as well as bring 

 the back plants nearer the roof an important matter in 

 plant-growing under glass. 



The Hip-Span is a useful form of house for building 

 against a wall too low to suit a lean-to. It is a com- 

 bination of the span and the lean-to, the short " hip " 

 or span at the back adding height and forming a con- 

 venient position for the ventilators. The above forms 

 of houses are those most in use, and any departure from 

 or combination of them is only carried out for the sake 

 of ornament. 



Next in importance to the building itself comes 

 the ventilation of the house. Elaborate ventilating 

 arrangements are by no means necessary, but provision 

 must be made for an ample supply of fresh air when it is 

 needed. By an ample supply I do not mean that there is 

 need for many different sets of ventilators, for these 

 often lead to draughts which are inimical to plant life and 

 breeders of mildew. Ample means of admitting air 

 must be given at the apex of the roof, and these roof- 

 ventilators must be continuous throughout the whole 

 length. Those houses which have some of the roof- 

 lights fixed and others made to open are sure breeders 

 of insect pests, besides endangering the plants beneath 

 such fixed lights by scorching. Too much importance 

 cannot be placed on the value of ample top ventilation, 

 as the air may thus be entirely changed without creating 



