20 CIRCULAE NO. 124, BUREAU OF PLANT INDUSTRY. 



weather and growth ])revailing during the seasons when ruptures of 

 the rind are ])revalent; that is, the facts observed liave been ]>ieced 

 together and the gai)s existing in our knowledge liiled ui by assump- 

 tions in such a way as to make a more or less complete story. This 

 theoretical explanation is only provisiona,l and awaits the results of 

 experimental examination before it can be considered a real explana- 

 tion. 



Many orange rinds sustain ru])tures (hiring or- after a prolonged 

 wet period following a drought which prevailed while the fruit was 

 making the latter part of its growth. The growing weather follow- 

 mg such a drought causes the jnilp to renew its growth and distend 

 the rmd. Smce the tissue of the inner rind, or rag, loses its vitality 

 before that of the outer or oil-bearing portion, its stretching capacity 

 is more limited and, therefore, more often ruptures, while the outer 

 rind becomes smiply more distended. However, when wet weather 

 prevails throughout the summer, as in 1912, the growth of the pulp 

 may be practically continuous, but, owing to the fact that such a 

 wet season is accompanied by the development of ammoniation and 

 melanose, the outer rmd loses its capacity for continued growth and 

 distention and therefore splits. Wlien the outer rind is bright or 

 unmjured, it may be stretched to meet considerable mcrease in the 

 size of the pulp mass; and if ruptures occur under such conditions 

 usually only the inner rind, or rag, is ruptured, resulting m what is 

 known as creased fruit. In either case the rmd of such fruits is 

 found to be very tight or under a very high internal pressure at the 

 time the ruptures occur. 



If oranges which have an internal growth-and-sap pressure almost 

 great enough to burst the rind were placed in a strong air-tight 

 vessel into which more air is pumped imtil the air pressure inside the 

 vessel is much higher than that outside, the rind on the inclosed 

 oranges would become fairly loose, simply because the air pressure 

 on the outside of the oranges (in the vessel) is now much greater 

 than the growth-and-sap pressure inside the oranges. On the other 

 hand, if, instead of pumping more air into the vessel containing the 

 oranges, air is pumped or drawn out so that the air pressure inside 

 the vessel is much less than the pressure outside, the expansive 

 forces inside the oranges (growth-and-sap pressure) will be so much 

 less restrained by the diminished air pressure surrounding the in- 

 closed fruits that their rinds will burst. In other words, if the pres- 

 sure in the oranges has reached a height wliich is almost sufficient 

 to result in creasing or splitting and then a period of low barometer 

 or low atmospheric pressure comes on, there are almost certain to be 

 many split or creased fruits, while a rise of the barometer or an in- 

 crease in the atmospheric pressure would probably have prevented the 



[Cir. IL'41 



