THE FUNCTIONS OF RADIATION IN THE PHYSIOLOGY 



OF PLANTS 



II. SOME EFFECTS OF NEAR INFRA-RED RADIATION ON PLANTS 



By earl S. JOHNSTON 

 Division of Radiation and Organisms, Smithsonian Institution 



(With Four Plates) 



Experimental results bearing on the influence of near infra-red 

 radiation on plant growth and coloration are presented and discussed 

 in this paper. Plants were grown under two different radiation dis- 

 tributions of equal visual intensity, one limited entirely to visible 

 radiation, the other including a large amount of energy in the near 

 infra-red. These preliminary experiments are a part of the program 

 being undertaken by the Smithsonian Institution bearing upon the 

 functions of radiation in various plant processes. A description of 

 the special equipment (see pi. i) that has been developed for the 

 study of the effects of radiation upon plants grown under controlled 

 conditions has been given in another publication (5).^ 



CULTURAL METHODS 



The tomato plant was selected for these experiments because con- 

 siderable work (12, 13, 14) had already been done with it in water 

 culture and many of its growth characteristics are known. Further- 

 more, it has been used as an indicator plant (10) for determining the 

 deficiency of certain fertilizer elements in the soil, and it responds 

 very quickly to unfavorable atmospheric conditions. Because of its 

 quick response to slight environmental changes its behavior is an 

 excellent criterion of those conditions. 



Tomato seeds of the Marglobe variety were germinated between 

 layers of moist filter paper in a covered glass dish at a temperature 

 of 25° C. When the roots had grown to a length of 2 to 10 mm 

 the young plants were transferred to a germination net. This net 

 was made by stretching two pieces of paraffined cotton fly-netting 

 over a circular glass dish 19 cm in diameter by 10 cm deep. The 



^ Numbers in parentheses refer to the list of Hterature cited, found at the end 

 of this paper. 



Smithsonian Miscellaneous Collections, Vol. 87, No. 14 



