RADIATION AND RESPIRATION 1067 



based largely on the data reported by Reich from numerous but uncon- 

 firmed experiments with one organ of a single species of plant. 



As for the physical basis of this effect by beta particles, there has been 

 a report by Stoklasa and P6nkava (21) which contains a suggestion. 

 Contrary to the evidence just cited, they seem to believe that radium 

 radiation increases the rate of respiration, but this may only correspond 

 to the temporary acceleration from short exposures, for they used very 

 small amounts of radioactive compounds. It is their claim that the 

 beta particles act on the glycolytic enzymes and thus cause the inter- 

 mediate labile products of respiration to be oxidized more rapidly. In 

 support of this idea they point out that forms which show the highest 

 rates of respiration are also richest in potassium salts. 



This discussion may have an important bearing on the normal proc- 

 esses of cellular respiration, but the amount of radium radiation 

 involved is so small in plants and in the experiments of Stoklasa and 

 Penkava that the results are hardly comparable with those of other 

 workers. However, if it be true that there is an effect on certain enzymes, 

 the depression in respiration reported for the seeds and seedlings as the 

 results of exposure to strong radium radiation may be due to a result 

 akin to fatigue or an injured enzymatic mechanism wdthin the irradiated 

 cells. 



Heat Effects. — In addition to radiation by waves of the length of 

 visible light or shorter, it is also possible for longer waves to influence 

 plant respiration. This is the familiar heating effect of waves of these 

 lengths, including the infra-red. However, it is also possible for the 

 shorter waves to give the same effect if and when their radiant energy is 

 transformed into heat. 



The influence of this heat upon respiration is so well known and 

 appreciated that httle need be said about it here. The resultant increase 

 in temperature within the tissue which interrupts and absorbs this 

 radiant energy always causes an increase in the rate of respiration up to 

 the point where the protoplasm is injured or killed by the high tempera- 

 ture. In any experiment in which radiant energy is absorbed by the 

 plant material or container, provision must be made to remove the heat 

 thus trapped, by the use of some device like a water bath to insure con- 

 stant temperature. If infra-red or longer waves are emitted by the 

 source of radiation, such as a mercury-vapor lamp for ultra-violet, such 

 waves can and should be filtered out by a water cell or similar material 

 which will transmit the desired waves but not those longer than light 

 waves. 



The quantitative statement of this heating effect is contained in any 

 one of the temperature coefficients, of which the Qio ratio of the 

 van't Hoff equation has the widest usage. For respiration, the Qio or ratio 

 of rates at two temperatures which differ by 10*'C. is between 2 and 3, as 



