01-01-2004, 12:03 AM
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Walnuts and their allies
In article ,
[Mike Lyle] wrote...
What advantage do walnuts and their relatives gain from having the
kernels of their nuts such an unusual shape? From my non-walnut point
of view it seems that having so many sticking-out bits increases the
risk of mechanical damage and drying-out.
Good question. But of course the lobes and sticking-out bits
are kept fairly safe inside the shell, even after germination.
[The seedlings are of the hypogeal type in the familiar members
of the walnut family].
One thought that occurs to me is that lobed and dissected food-storage
tissues in seeds may be partly protected from insect damage. There are
teh familiar plates of not-so-edible, fairly hard tissue between the
lobes. An insect attacking the seed might tend to confine its activities
to a single lobe, or at least it would have a harder time making a meal
of the whole seed.
Although the lobed seed structures in the walnut family [Juglandaceae]
are the cotyledons of the seedling, the situation is reminiscent of
something called "ruminate endosperm" that is found in many other
families of flowering plants. In these plants the food-storage tissue
of the seeds is endosperm, which is lobed and dissected by plates and
strands of hard inedible sclerenchyma tissue.
An insect trying to eat such endosperm might have difficulty tunneling
through it, compared to one living in a similar seed without ruminate
[meaning ="chewed"?] endosperm.
A ref:
Occurrence and taxonomic significance of ruminate
endosperm.Bayer Clemens Appel Oliver
1996 The Botanical Review;
Ruminate endosperm is characterized by its uneven and enlarged
surface. A list of 58 angiosperm families in which this trait is
known to occur is presented. The simultaneous presence of
different rumination types in angiosperms and even within single
families leads to the conclusion that ruminate endosperm has
originated several times in parallel. Therefore, the mere occurrence
of rumination does not provide evidence for phylogenetic
hypotheses. Nevertheless, rumination features can provide
valuable characters for taxonomic purposes, [snip]
cheers
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