54 GREENHOUSES 



Uneven Span Houses. The uneven dis- 

 tribution of light in even-span houses 

 running east and west early led to the 

 experiment of cutting off the north one- 

 fourth, so as to make an uneven or three- 

 quarter span house. The following advant- 

 ages are claimed for these houses: (i) They 

 secure a more even distribution of direct sun- 

 light to all plants. (2) The north span ad- 

 mits indirect light which insures better re- 

 sults than may be secured from a lean-to 

 house. (3) The heat is more evenly distri- 

 buted than in a lean-to house. They are 

 often used in growing roses and other plants 

 requiring a maximum of light. The con- 

 struction of uneven span houses has been 

 varied from time to time, the general ten- 

 dency being to lower the north wall to ap- 

 proximately the height of the south wall. 

 This arrangement insures even better distri- 

 bution of light and does away with the neces- 

 sity of elevated benches. 



Uneven span houses are sometimes used 

 for growing lettuce and other vegetables di- 

 rectly on the ground instead of in benches, 

 especially on sloping locations. Modern 

 greenhouses are so much lighter than the 

 older types that the advantages of the un- 



