Light in Greenhouse Culture 59 



and equal conditions of care and culture were ob- 

 served in all of them, approaching natural condi- 

 tions as nearly as possible. The temperatures in 

 these houses are given in Table 7. 



Table 7 



Time of day 



White 



Red 



Green 



Blue 



7:30 A.M. 



Degrees 

 32.0 



Degrees 

 31.0 



Degrees 

 30.7 



Degrees 

 295 



8:30 A.M. 



40.0 



39.5 



370 



35.0 



10:30 A.M. 



49.0 



46.0 



41-5 



40.0 



12:30 P.M. 



42.0 



40.0 



39.0 



38.0 



2:30 P.M. 



41.0 



40.5 



40.3 



40.2 



4:30 P.M. 



30.0 



30.0 



30.0 



30.0 



It is evident that the ability of the glass to absorb 

 the sun's rays determines the heat in the hothouses. 

 All rays are able to pass through white glass, which 

 explains why the highest temperatures were found 

 in this house. The lowest temperatures were found 

 in the blue house, blue having the greatest absorb- 

 ing power. It is striking that the temperature was 

 apparently the same in all the hothouses during 

 the cloudy weather and when the sun's rays did not 

 penetrate directly. 



Plant Growth Influenced by the Color of 

 THE Glass 



Experiments on sensitive plants showed the fol- 

 lowing results: Plants placed in a red house de- 



