844 



BIOLOGICAL EFFECTS OF RADIATION 



be able to carry on limited photosynthesis when placed under infra-red 

 at night. This test was made recently as follows: 



Four pots of buckwheat seedlings were grown in a greenhouse during 

 the months of December and January under solar illumination during 

 the day and under the infra-red from a 500-watt lamp each night. A 

 composite filter made up of Coming's heat-transmitting glass 4 mm. in 

 thickness was used to remove the visible region. The transmission of this 

 glass has been indicated in a previous publication (1). The filter was 

 supported on a wooden stand a short distance below the lamp. The 

 distance from the lamp to the soil in which the seedlings were grown was 

 22 in. The lamp was fitted with an aluminum reflector for directing 



Fig. 1. — Buckwheat seedlings. D, at left, grown in darkness. I.R., at right, received 

 only the infra-red of sunlight. Note that there is no difTerence in the appearance of the 

 two. The green pigment chlorophyll does not develop under infra-red. 



the radiation downward so as to cover the filter effectively. A second 

 set of four plants was grown beside the first set and was treated similarly 

 except that a sheet of galvanized iron was used under the second lamp 

 instead of the infra-red filter. The seedlings were grown for two weeks, 

 then were cut down and green and dry weights determined. This test 

 was repeated during January and February, In each test the seedlings 

 were grown from seed for approximately two weeks before they were 

 placed under the test conditions. The results are shown in Table 2. 



The seedlings in the first test were grown during a period of cloudy 

 weather and produced much less dry weight than those in the second test. 

 There is no evidence, however, that those grown under infra-red each 

 night produced more dry weight. There is some indication that the 

 plants receiving infra-red weighed less than the controls under sheet 

 metal. This might be expected since respiration would probably be 

 higher under the infra-red conditions owing to the higher temperature 



