56 MISC. PUBLICATIOIT 16 8, U.S. DEPT. OF AGRICULTUKE 



The spotting is brown in color and usually only superficial and 

 is most pronounced on russetecl areas of the skin. It sometimes 

 occurs in bands crosswise of the fruit, corresponding to the corruga- 

 tions in the paper liner (pi. 18, C), but usually appears merely as 

 irregularly shaped brown spots i/4 to 1 inch in diameter. Varieties 

 on which it has been found are Winter Nelis, Bosc, and P. Barry, 

 all of which show more or less russeting. It has not been found on 

 smooth-skinned pears, although a dark discoloration on Anjou and 

 Bosc pears, the result of pressure or rubbing against the paper liner, 

 the box, or other pears, has sometimes been confused with it. 



Silicate injury seems to have no eifect on the keeping quality of 

 the fruit. 



In some of the corrugated paper used for liners for pear boxes, 

 sodium silicate has been used as a binder to hold the corrugated and 

 the flat sheet together. The silicate contains a small percentage of 

 free alkali, and there is abundant evidence that this is the constituent 

 that causes the injury. Moisture is necessary, and in many instances 

 it seems to be present in sufficient amounts within boxes packed with 

 pears to cause some of the alkali contained in the paper liners to 

 go into solution and produce injury. 



The spotting can be avoided by using liners that do not contain 

 free alkali from sodium silicate or any other source. {197.) 



SMOTHERING INJURY 



Attempts have been made from time to time by various persons 

 and commercial organizations to keep pears and other fruits in a 

 fresh state by holding them continuously in closed containers in an 

 atmosphere of nitrogen or carbon dioxide or in air containing a high 

 percentage of carbon dioxide. In some instances a partial vacuum 

 is produced in the container before the carbon dioxide or nitrogen is 

 introduced. 



The results obtained from this " gas-storage " method are not al- 

 ways satisfactory, for the reason that it is impossible to bring fruits 

 to a physiological standstill merely by excluding oxygen from the 

 air surrounding them. Oxygen is essential to the normal life proc- 

 esses of plants, and if it is not present, fruits and other live plant 

 parts obtain it by breaking down their own tissues and thus eventu- 

 ally destroy themselves or at least undergo serious deterioration 

 (pi. 18, A). 



Injury is proclucd also if the concentration of carbon dioxide in 

 the container is high from the beginning, or if it becomes high as a 

 result of the respiration of the stored fruit. The latter condition 

 readily develops in containers when no provision is made to keep 

 the composition of the atmosphere in the container constant or to 

 provide sufficient oxygen for the fruit. 



Different species of fruits vary in their tolerance for carbon di- 

 oxide. The flavor and condition of some kinds of fruit are very 

 readily affected by even 24 hours' exposure to concentrations of 25 

 percent or more of the gas. This is particularly true of peaches, 

 strawberries, raspberries, and similar aromatic fruits. Other kinds 

 like pears, grapes, and plums are more resistant but not sufficiently 

 so to withstand continuous exposure to such high concentrations of 

 carbon dioxide. 



