the heavy, Hght obstructing frames very poor Hght was obtained. 

 Some improvement has been made in the roof angles also, houses 

 with larger angles giving better light; in fact, the more closely 

 the angle of the roof coincides with the right angle to the sun's 

 rays the more light the crop receives. Low, flat hotbeds, which 

 are usually covered with small, dirty, inferior glass, furnish a good 

 illustration of poor angles, the light obtained being extremely 

 poor. The old type of house, built of sashbar glass, may still be 

 found occasionally. The glass in these houses is of all sizes and 

 shapes, running from 2 to 5 inches wide and 2 to 7 inches long, 

 and is sometimes lapped more than an inch. Not infrequently 

 50 percent or more light is shut out. With the development of 

 the greenhouse industry larger and better glass began to be used, 

 until now we find 16 x 24, 20 x 30 and 24 x 24 inch glass in use. 

 Practically all this glass is second quality, double thick, although 

 in some parts of the country much third quality glass is used even 

 now. The most common size is 16 x 24 inches. This is usually 

 run lengthwise of the roof, although occasionally crosswise, i.e., — 

 the sashbars are placed 24 inches apart, in which case one sashbar 

 is saved every 4 feet. In a house 30 feet wide this would be a 

 saving of about 1484 square inches of shadow casting material for 

 each 4 feet in length. In a house 400 feet long this saving would 

 amount to considerable, especially wheii the ends and sides are 

 constructed in the same way. Where larger glass is used, less 

 frequent lapping effects a saving in light. 



Comparatively little 24 x 24 and 20 x 30 inch glass is now used, 

 experience not justifying its use in all cases. Mr. Richard Hit- 

 tinger's* large house, 40 x 600 feet, is glazed with 20 x 30 glass, 

 but this house is so thoroughly built and purlined that it has 

 given less trouble from breakage than his old houses, in which 16 

 X 24 inch glass was used. When a large glass breaks, however, 

 it costs more to replace it even if the original cost of the glass is 

 the same per square inch. Our experiment house, built under 

 our direction, is glazed with 24 x 24 inch, No. 2 double thick glass. 

 Its severe exposure makes it unsatisfactory in some ways, and we 

 have had considerable breakage, especially on the northwest side 

 of the house in the direction of the prevailing winds. Such a 

 house would be much more satisfactory in a sheltered location. 



The Pierson "U-Bar" type of construction employs this kind 

 of glass. The economical use of large glass depends on the rigidity 

 of the frame, and this type of house is provided with a rigid iron 

 frame and iron and wood sashl3ars. The amount of shadow pro- 

 ducing material is much less than where 16 x 24 inch glass is used. 

 However to support large glass, a house must be thoroughly con- 

 structed and well purlined to prevent breakage, as has already been 

 stated. Many of the older houses were defective in this respect, 



*Mr. Hiltinger, whose range of houses is located at Belmont, Mass., is one of the largest 

 lettuce growers of Massachusetts. 



