🚀 go-pugleaf

In article <34C555B3.F6C@ibm.rhrz.uni-bonn.de>, 
unc805@ibm.rhrz.uni-bonn.de wrote..
>
>Hello,
>can anybody tell me what the "nut" inside a ginkgo seed is produced
>from?

>The outer fleshy layer is the sarkotesta, the stony middle layer the
>sklerotesta and the third is dry and papery (is there a special name for
>it?). All three of them are build up by the integument (if my
>information is right).
>
>But what is the "nut inside". If I am right, the egg cells are sometimes
>fertilised when the seed has already fallen to the ground. So the "nut"
>can not be the embryo. But what is it, and why can an egg cell be
>fertilised and develop the embryo when the seed has already fallen to
>the ground?

As in other gymnosperms, the "endosperm"-like fleshy tissue inside the 
seed is the female gametophyte [megagametophyte].  I'm not sure that it 
is still considered true that fertilization commonly occurs off the tree, 
but I see no reason why a pollinated ovule with growing pollen tubes 
couldn't fall off the tree and still complete its development.  The 
cycads and Ginkgo are the only living seed plants still with flagellated 
motile sperm cells.

>Ginkgo is a fascinating Gymnosperm plant but some things are hard to
>understand.

cheers