Light in Greenhouse Culture 71 



must be worked out for each specific crop. Ordi- 

 narily, under greenhouse conditions, shading is ac- 

 complished by means of whitewashing the glass of 

 the hothouse. It would seem more desirable to use 

 chambray, light chambray or voile cloth instead of 

 whitewashing. The cloth could be installed on a 

 system of rollers, so that when shading is necessary 

 it could be spread out on the glass and when not 

 needed it could be rolled up again. This would 

 enable the greenhouse man to retain the full amount 

 of normal light on cloudy days, an advantage which 

 cannot be obtained when the glass is whitewashed. 

 The substitution of cloth for whitewashing offers 

 a good field of experimentation, both for the labora- 

 tory and for the practical man. 



Heat Requirement 



The heat requirement of indoor crops demands 

 the closest attention and study. As is well known, 

 no two crops require the same temperature for their 

 maximum development and production. Moreover, 

 the same plant requires different temperatures in 

 its various stages of growth. To appreciate thor- 

 oughly the relationship of heat to plant life, we 

 may liken the plant to a steam engine. With very 

 slight steam pressure, the engine remains "dead," 

 because it is not able to overcome the friction of 

 its own parts and hence is capable of no work. 

 With the proper amount of steam pressure, the 

 engine is capable of a maximum amount of work. 



