SOME INFRA-RED EFFECTS ON GREEN PLANTS 



845 



of the plant tissues brought about by the radiation. The data are not 

 conckisive as regards this point. 



Table 2. — Green and Dry Weights of Buckwheat Seedlings Grown under 

 Sunlight during the Day and under Infra-red Each Night during a 



Period of Two Weeks 



In this connection the work of Johnston (14) is especially significant. 

 He grew tomato plants in four chambers using 1000- and 1500-watt 

 lamps. Temperature and humidity were accurately controlled by 

 recirculation of air. Two types of filters were used and two illumination 

 values as measured by a Weston photronic cell with a Corning heat- 

 absorbing filter. The filters were (a) Pyrex glass plus water 1.5 cm. in 

 thickness, and (6) Pyrex glass plus water 1.5 cm. plus Coming's heat- 

 absorbing glass 8 mm. thick. The water-layer filter transmitted to 

 \14,000 A. The other filter was designed to have a transmission curve 

 which coincides approximately with the sensitivity curve of the human 

 eye. Under one filter of the Pyrex-plus-water type the illumination was 

 339 foot-candles, under the other of this type it was 1966 foot-candles. 

 The corresponding illuminations under the two heat-absorbing glass- 

 plus-water-type filters was 359 and 1966 foot-candles. The dry weight 

 of tissue produced was as follows: 



Pyrex plus water 



Pyrex plus water 



Heat-absorbing glass plus water 

 Heat-absorbing glass plus water 



Foot-candles 



339 

 1966 



359 

 1966 



Dry weight, 

 mg. 



126 



426 



16 



199 



