104 



EXPERIMENT STATION RECORD. 



shows the temperatures observed in the different houses on August 20, 

 1895: 



Temperature of interior of hothouses with white and colored (/lass. 



Time of day. 



7.30 a. m . 

 8.30 a. m . 

 10.30 a. m 

 12.30 ]>. m 

 2.30 j). m 

 4.30 p. in 



Blue. 



Beg.C 

 29.5 

 35.0 

 40.0 

 38.0 

 40.2 

 30.0 



From the above table it will be seen that the temperature of the hot- 

 houses decreased as the extreme right of the spectrum was approached. 

 The temperature was the same in all the hothouses during cloudy days 

 or when they did not receive the sun's rays directly. The decrease of 

 the temperature in the blue house, as compared with the white, is 

 explained by the fact that the absorptive power of the glass of the 

 hothouses increased as the violet extremity of the spectrum was 

 approached. The ability to absorb the sun's rays determines the heat 

 in the hothouses. All rays traverse the white glass, and it is therefore 

 in this house that the highest temperature was found. ( )n the other 

 hand, blue glass has the greatest absorbing power, and the hothouse 

 covered with blue glass had therefore the lowest temperature. 



In 1895 sensitive plants, grown from the same lot of seed and equally 

 vigorous, were placed in each hothouse. Their height at that time was 

 0.027 meter. The plant placed in the red house developed extraordi- 

 narily and attained a size lifteeu times as great as that in the blue 

 house, where the plants remained nearly stationary. The red light pro- 

 duced the effect of a chemical fertilizer, although in this case actinic 

 rays were absent. These plants were all equally cared for. The sensi- 

 tiveness of the plant grown in the red house had attained such a degree 

 that the slightest movement or breath was sufficient to cause the clos- 

 ing of the leaflets and the drooping of the pedicels. The sensitive- 

 ness diminished under the white or green color, while under the blue 

 light the plant was almost insensitive. The plant in the red house 

 blossomed September 24. In the white house it increased in stockiuess 

 and was very vigorous but did not increase in height. It showed 

 flower buds, but they did not open. The plant under the red glass had 

 a lighter colored foliage than that under the white. The foliage was 

 paler than that under the green, while the blue was much darker. 

 The difference of the temperature between the hothouses was not very 

 great. There were, nevertheless, several degrees difference between 

 the white and the blue. The intensity of illumination decreased in the 

 same proportion as the temperature rose. The height of the plants in 

 the different houses after an experiment of 3 months was relatively as 

 follows: Blue hothouse, 0.027 meter; white hothouse, 0.1 meter; green 

 hothouse, 0.152 meter, and red hothouse, 0.12 meter. 



