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I cut an underripe avocado in half and put half of it, without the pit but with the peel, in the refrigerator. A day later, I see very small black bumps along the cut surface. What are they? What causes them?

A view.

Another.

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If this is off-topic here (which I doubt), please consider migration to Seasoned Advice in lieu of outright closure. –  msh210 Jul 26 '12 at 5:04
    
That avocado does not look underripe to me... –  nico Jul 26 '12 at 6:40
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This is on-topic, the answer is about plant anantomy –  Richard Smith Jul 26 '12 at 8:05
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@nico, the parts closer to the pit were too hard to be palatable (to me), so either it was underripe or I like avocados overripe. –  msh210 Jul 26 '12 at 15:44
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1 Answer

up vote 13 down vote accepted

It looks to me (although I'd want to use a microscope to check) like the black dots are xylem. When you cut the fruit, you've severed the xylem and also exposed the flat surface. Three main things have then happened:

  1. The increased surface area has led to the 'fleshy' part of the fruit contracting as the cells dehydrate.
  2. The stiffer, lignified xylem tubes have retained their structure and have not contracted with the rest of the fruit, so they've become exposed.
  3. The exposed xylem have blackened due to oxidation - this eventually happens to all the flesh but, again speculating here, the oil in the fleshy tissue might protect it from oxidation longer than the exposed xylem which don't have the oil coating.
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+1, and thank you! –  msh210 Jul 26 '12 at 15:42
    
+1, interesting reasoning. –  Luke Jul 26 '12 at 16:11
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