Okay, just spoke to him.
He says the effect of the pollen on seed size is "very little" -
sometimes if the pollen is bad then it will make small seeds, but
otherwise it has almost no effect on immediate seed size (though
obviously it can affect the size of the seed in the next generation).
One of the reasons for this is that the mother plant largely shuts down
the genes from the pollen so they don't get expressed until the plant
starts growing. Another is that the food supply to the developing seed
is controlled by the mother plant.
If the tree is "having a good time" it will produce bigger seeds, and
this is the most influential factor in seed size. It's also why some
seeds in a catkin are larger than others - they have a better food supply.
He reckons that 20 generations of selection might see a significant
increase in seed size in A. glutinosa, but he wouldn't be drawn on an
estimate of how much.
"He", btw, is professor emeritus of botany at Oxford, and keeper of the
botanic gardens and arboretum there. He was also a bigwig at Kew for a
while, don't know exactly what kind. He's one of, if not the, top
authorities on this in the UK - I won't post his name here, but you can
You should still choose bigger seeds, but going for the very biggest is
not likely to be useful in terms of their paternity.
-- Peter Fairbrother
I will have to bear this in mind for follow-on breeding work, but not
for first screening for bigger seeds: the tree whose seeds I am
sampling now had a chain of ancestors going back...
It is MOST UNLIKELY that I would find THE TREE in which a mutation
occurred. If a mutation has occurred, that mutation will probably
appear in several trees which are not too far apart, the two will
fertilise each other (though most of the pollen will come from
unrelated trees) so a very small number of mutated seeds will be found
in both trees. This is the kind of reason why it is so important to be
able to screen through a very large number of seeds. And of course,
some of the seeds which I think have promise will turn out badly. You
must accept that with bulk screening.
I'll do that when I've got the immediate rush over.
No no no - even if you get a seed with big-seed mutations in both the
pollen and the mother, it *won't* be any larger than a seed whose mother
has a big-seed mutation and whose father doesn't.
That's what I've been trying to tell you. Do you understand it? Please??
I have more useful stuff to say, but you have to understand that first.
It's important to screen a very large number of trees, not seeds. That's
what the forestry commission do.
What you want to do is look for mothers who produce big seeds, not for
the biggest seeds.
(there most likely won't actually be one mutation, and a double mutation
isn't necessarily going to give big seeds - or any seeds at all - but
-- Peter Fairbrother
I have a rheostat (R S Components 170-304) and I have on order a speed
controller (Type KC5225 from Jaycar WWW.JAYCAR.COM.AU)
The likely duty cycle is;-
Pull cones off tree 2 minutes
Crush cones 1 minute
Run seed sorter 1 minute
Walk to next tree 1 minute
I have a 1.2 AH lead-acid battery. It's not too heavy. I can't see
myself running out of juice at this rate, but I could have 2, one for
the morning, one for the afternoon.
What you may want is uniform flow.
The way that is achieved in a decent wind tunnel is to have a contraction in
the tube with a '2q' screen across it.
Called '2q' because the pressure drop across it is twice the dynamic
pressure (0.5?V^2) of the approaching airflow
Can't remember the spec.of such a mesh for sure but it's pretty fine stuff.
Something like 30 mesh 32 gauge
Bigger seeds have more weight and more drag - which wins?
Perhaps I should have followed some of the links given.
I don't understand this. Should this mesh be at the intake from
"still" air or where the inlet taper changes to parallel sides? I have
1 mm wire mesh. Maybe I could get different if I knew what was wanted.
For spheres of the same density, the bigger spheres fall faster. It's
a matter of weight/surface area.
For your simple shape the best you can do is to place the mesh at the inlet.
30 mesh means 30 wires per inch and 32 gauge (SWG) is about 0.010 inches (
0.25mm) in diameter
It's actually a matter of weight/frontal area.
Surface area is proportional to 'width' cubed.
Frontal area is proportional to 'width' squared
The conclusion is the same provided the seeds have the same density.
My question really boils down to questioning if the seeds have the same
density independent of size.
I'm curious that no one has suggested using a cyclone. A light tin can
is easily transportable and by sizing the cone angle and pipe
diameters appropriately they can be made to be very selective and have
no filters or screens to get blocked or contaminated.
It's donkey's years since I did any analysis on such a thing, but I
should imagine it's easy enough to unearth if you look.
It's a possible design. But air would flow into the outlet at the
bottom for the heavies so I would have to put a glass jar at the
bottom to collect them. However I have gone so far down this route
that I don't want go another way.
I don't see how they could NOT have the same density independent of
size. But it doesn't matter. I want seeds that contain food material,
if a seed contained a lot of fluff, I wouldn't want it anyway.
Actually it's not exactly that, but a complete analysis would take
several pages of math. It's close though.
Take a half-full jar of honey or syrup and shake it vigorously, then put
it down. The big bubbles will rise fast, but the small bubbles will take
a long time to rise.
It's the same with seeds in air, except the other way up, and honey is
thicker than air.
-- Peter Fairbrother
For the same shapes so is surface area and Michael mentioned that.
Indeed but I was conceding that althought Michael's analysis was flawed,
heavy seeds fall faster if of the same density.
You don't spend 30 years working in wind tunnels without learning some of
Mind you that was a while ago now so can't claim to remember everything!
Fine. Now the next stage of the design.
My sorting tube has an internal diameter of 2.5 cms and the fan has an
internal diameter of 8 cms, and I want to connect them with an
inverted cone - actually an inverted pyramid because it will be
It would be nice for the seeds to settle in bands of different size in
the cone that joins them, but in such turbulent flow that's asking for
So failing that, what I want to do is to do it in an energy efficient
way, and that means an evase. What angle should it be? There is plenty
of vertical space. What should the expansion angle be? It will
probably be expressed as 1 in x rather than in degrees. Google
acknowledges the meaning of the word, but I can find no way of
Why for goodness sake ?
Starting with two circles it's easier to make a cone.
It will also be more efficient that some odd thing with squares crudely
It could be reasonable with transition pieces for circle to square at each
end but complicated to design and make.
7 degrees included angle between the walls
As a cone it will be 45 cms long
Read all the helpful suggestions. As far as I can see, no-one has yet
suggested a sideways air current.
Since (as someone pointed out) the weight varies as the cube of the
linear dimensions, and the cross-sectional area varies as the square, a
bigger seed would be less deviated by a cross current than a smaller
one, so the distance from the vertical axis at which the seed hits the
ground should vary inversely as the size of the seed.
You could try this quite easily, and (assuming it works) the apparatus
should be quite portable. The cross-wind would have to be pretty
constant, and the thing shielded from extraneous winds.
The idea is quite reminiscent of the method used in a mass spectrometer,
with an electromagnetic field acting as the "side wind".
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