why are fruits round

Janice M. Glime jmglime at MTU.EDU
Tue Nov 26 12:21:13 EST 1996

  Since this is turning into an interesting thread of speculation, I will
pose some additional possibilities.  I watched my flying squirrel carry
off a variety of nuts and when she got a macadamia nut, it was too round
and smooth for her to keep hold of it when she did a backflip onto the
rafter.  Time after time, but not every time, she dropped it and had to go
hunting for it.
  It may be that being round is an advantage for fruits to avoid being
carried off by some mouth sizes that do not effectively disperse seeds,
but rather eat and crush everything.  
  I suspect, however, that there is a more fundamental reason for the
roundness that relates to mode of development.  If there are 5-many flower
parts, especially petals and sepals, around the developing ovary, that may
mold the tissue into a round shape in some species, depending on timing
and number of carpels.  On the other hand, a 3-carpelled ovary, surrounded
by 3 petals or 6 tepals in 2 rows, may be molded into three parts and
further supported in three edges by the number of carpels.  
  Is the term fruit in this question being restricted to those fruits that
are eaten by mammals and birds, or does it include all the dry fruits that
are more likely to be gnawed on by insects?  I still am not convinced the
basic premise is true.
 Janice M. Glime, Professor  
 Department of Biological Sciences
 Michigan Technological University
 Houghton, MI 49931-1295
 jmglime at mtu.edu
 FAX 906-487-3167 

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