398 GROWTH OF PLANTS 



cance of the use of this inhibitor in farm and commercial storage. In farm 

 storage there is no chance for close control of temperature, and it will not 

 be needed if the inhibitor is used. Only the portion of the fall crop to be 

 used after January 1 to 15 need be treated. In commercial storage there 

 will be a saving in refrigeration, and sweetening of the potatoes can be 

 avoided. Here, too, only the portion of the crop that is to be stored well 

 into the winter and spring should be treated. 



Physiological and Biochemical Effects of Carbon Dioxide 



Thornton has made extensive studies of the effect of CO2 in various 

 concentrations in the atmosphere over a wide range of temperatures upon 

 the biochemistry and physiology of various plants and plant organs. In 

 mass storage and in nature, plant organs or the living cells of plant organs 

 often exist in concentrations of CO2 far above that of the atmosphere, due 

 to respiration of the organs and the accumulation of the CO2 about or 

 within them. Soil ah ^^ sometimes has a considerable content of CO2, and 

 plant organs growing in water or water-logged soils may have an internal 

 atmosphere ^^ rich in CO2. Massive organs such as fruits, tubers, fleshy 

 roots, and tree trunks,^^ when existing individually in the air, may have 

 an internal atmosphere rich in CO2. In such organs the percentage of CO2 

 in the internal atmosphere generally rises as the temperature rises. Accord- 

 ing to Magness,^'^ the internal atmosphere of apples held individually in the 

 air at 2° C (36° F) had 6.7 per cent CO2 and 14.2 per cent O2 and at 30° C 

 (86° F) 21.4 per cent CO2 and 3.2 per cent O2. For carrots at 11° C (52° F) 

 the internal atmosphere was 12.2 per cent CO2 and 10.9 per cent O2, and 

 at 24° C (75° F) it was 28.6 per cent CO2 and 5.2 per cent O2. Bartlett 

 pears ^^ in storage in boxes at the freezing point or a little below had an 

 internal atmosphere of about 6 per cent CO2 and 19 per cent O2. In similar 

 storage at 60° F (16° C) the CO2 was 24 to 33 per cent and the O2 8 to 

 10 per cent. A Rome Beauty apple 9.1 cm. in circumference, hanging on 

 the tree just after the middle of June, shows an average internal atmos- 

 phere 2^ of 32.4 per cent CO2 and 5 per cent O2. At earlier and later periods 

 the CO 2 content is lower — very much lower at the late stages of develop- 

 ment. 



Because of the facts just stated, there are two situations that ought to 

 be kept in mind in describing Thornton's work on CO2 effects. First, 

 while the concentrations used in his experiments are often higher than those 

 existing in nature or in practice, those sometimes existing in nature and 

 practice are sufficiently high to bring about easily measured metabolic 

 effects in plants; as a result, CO2 may be considered as one regulator of 

 plant metabolism. Secondly, in the experiments to be described, the con- 

 centration of CO 2 given is always that in the air surrounding the plant or 

 plant organs being studied, and not that in the internal atmosphere of 

 the plant organs themselves. Consequently, the actual concentration 

 within all massive organs like fruits and tubers is considerably higher than 



