MISCELLANEOUS 399 



recorded. In the case of thin organs Hke leaves and petals, of course, there 

 is not so much difference. 



Effect of high concentration of CO2 on plants in storage. The early 

 studies ''^- " were for the purpose of determining the concentration of CO2 

 in the surrounding air that various plant organs tolerate wdthout injury 

 while being shipped or held in storage. This was for the purpose of deter- 

 mining the precautions that must be taken to prevent CO2 from the Dry 

 Ice as a refrigerant from reaching the fruits and vegetables in transit. In 

 general, plant organs withstand higher concentrations of CO2 when they 

 are firm and solid than when they are soft and ripe ; this is also true when 

 there is no surface moisture. In general, they endure high concentrations 

 near the freezing point better than at higher temperatures. There is one 

 exception to the latter : the flavor of Walters variety of grapefruit is greatly 

 impaired in 64 per cent CO 2 at 0° to 4° C (32° to 39° F), but is little im- 

 paired in the same concentration at 10° to 15° C (50° to 59° F). There is 

 a great difference in the concentrations endured by different plant organs. 

 At the freezing point tomato fruits will endure only 6 per cent for four 

 days mthout injury, lettuce 7 per cent for seven days, Bartlett pears 10 per 

 cent for seven days, and a number of plant organs only 15 per cent (mush- 

 rooms for four days, strawberries three days, and Talisman and Pearson 

 rose flowers seven days). On the other hand, some plant organs endure 

 very high concentrations of CO2, especially at the freezing point: Delicious 

 apples 83 per cent for seven days, carrot roots 80 per cent for five days, 

 and rhubarb stalks 80 per cent for seven days. The other 32 fruits, vege- 

 tables, and flowers tested stand somewhere between these two groups in 

 their resistance to CO 2 injury. 



The effects of low, non-injurious concentrations of CO2 bring about 

 retardation of respiration and color and other ripening changes in certain 

 fruits. Such concentrations removed astringency in green bananas and 

 pears, and increased by four days the length of time various flowers could 

 be kept in cold storage without injury. High, injurious concentrations 

 impair the flavor of all fruits and some vegetables ; prevent changes in color 

 and flavor of banana, peach, and orange; kill growing tissues of asparagus 

 and potato sprouts; promote decomposition of exposed tissues of vegetables 

 that are high in moisture; cause internal discoloration and breakdo^\^l of 

 apple, pear, peach, potato, and tomato; and induce external discoloration 

 of pear, peach, and banana. 



Following these more general economic investigations, Thornton made 

 extensive studies of the effect of CO 2 in various concentrations upon the 

 growth and metabolism of plants. 



Effect on dormant seeds and buds. Recently harvested lettuce seeds 

 requu-e a temperature below 20° C (68° F) for germination in darkness and 

 below 26° C (79° F) for germination in light. Treating such imbibed 

 lettuce seeds ^^ for 65 hours with 40 to 80 per cent CO2 and 20 per cent O2 

 at 35° C (95° F) causes them to germinate later at this temperature. Even 



