6 BULLETIN -830, U. S. DEPARTMENT OF AGRICULTURE. 



for the same lots at room temperature ranged from 0.76 to 2.11 

 grams with a 60-micron needle. Similar differences in the pressure 

 required to puncture the warm and cold fruits were obtained when 

 the fruit was allowed to remain hi the ice box 24 hours. Washing 

 the berries in tap water did not appreciably affect their resistance to 

 puncture one way or the other. This may be due to the fact that the 

 berries were tested immediately on removal from the water, which 

 would preclude any appreciable cooling effect from evaporation. 



The results with Montmorency cherries were practically the same 

 as those with berries. Cooling the fruit increased its resistance to 

 puncture. 



From these results it is evident that the fruits used in the work are 

 much less easily punctured when cool than when warm. It seems 

 probable that this increase hi the resistance of the skin to mechanical 

 injury is an important factor in the results obtained by Ramsey, 

 Stevens and Wilcox, and Ridley in their work on the prompt cooling 

 and refrigeration of berries. It would seem also that the picking of 

 berries in the early morning when they are cool, as is quite commonly 

 practiced in some regions, would be decidedly advantageous, in spite 

 of the fact that at that time the berries are frequently wet with dew, as 

 no evidence was obtained that moist berries were more susceptible 

 to injury than dry fruits. 



No attempt was made to determine the reason for this increase in 

 resistance to puncture due to cooling. A possible explanation of 

 this phenomenon, which occurred to the writers, was that the surface 

 of the fruit might be covered with a wax which softened at the higher 

 temperatures but became harder and more resistant when cooled. 

 Another purely mechanical explanation is that the walls of the 

 drupelets or of the external cells of the fruits have a lower coefficient 

 of expansion than their contents. If this were the case, at higher 

 temperatures the walls would be under greater strain and would, 

 therefore, puncture more easily. This point deserves further inves- 

 tigation. 



In conclusion, it has been shown in this work with strawberries, 

 blackberries, black and red raspberries, and cherries that cooling the 

 fruit renders the epidermis more resistant to mechanical injury. 



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