Field of Science

Bean seed redux

You try your best, you really do, but it never seems to be  enough.  This is the single most commonly encountered error that TPP sees.  He has certainly corrected it in enough biology textbooks (always accurately identifies botanically ignorant authorship), and quite recently posted a lesson on bean seeds. Of course, no one should actually read the Huffington Post for their science reporting, and although memory fails TPP on the specifics, he's certain he has corrected Landess Kearns (the author) before.  So here it is once again, sorry, Landess you are incorrect in your identification of a peanut "embryo".
 The "little" nub at the right is identified as the peanut embryo.  WRONG!  What do you think those two big things are?  This peanut plant at the embryonic  stage consists of a pair of cotyledons that function in food storage, and they are attached the main axis of the embryo.  The pointy end to the right is the embryonic root axis and above the attachment point (node) of the cotyledons is at least one pair of heart-shaped true leaves (each neatly folded in half).  The whole DANG thing is the embryo; this illustration shows 
2 peanuts, 2 embryos.  At maturity there is no endosperm in this seed, just a seed coat (removed in this case) and the embryo.  The endosperm was absorbed by the embryo as it grew.  But so many textbooks say seeds have endosperm that this misconception continues, perhaps because people cannot grasp that at this embryonic stage two leaves are so much bigger than the rest of the plant. So Landess, here's a helpful hint: split peas aren't split!  But they still make good cotyledon soup. And please don't try to figure out "pine nuts" on your own.

No comments: