Pin, Thrum and Pollination

[Rodger Whitlock]

So do I understand correctly: thrum x thrum crosses are impossible while pin x pin crosses are less fertile and can produce only pins?

And in the latter case, is there a decline in vigour?

My understanding is that pin-pin and thrum-thrum crosses produce fewer seeds than pin-thrum crosses, but they are not totally sterile. Darwin studied this phenomenon in some detail in "The Different Forms of Flowers on Plants of the Same Species."

Please note use of the weasel phrase "My understanding is". As usual, I reserve the right to be proven wrong.

[Giles]

There is a detailed article about this: 'Pin and Thrum in Primula: Crosses, seed setting and vigour' by John Richards in the 'Alpines 2001' Conference Report.
I've scanned the Table.

[ashley]

My understanding is that pin-pin and thrum-thrum crosses produce fewer seeds than pin-thrum crosses, but they are not totally sterile. Darwin studied this phenomenon in some detail in "The Different Forms of Flowers on Plants of the Same Species."

Please note use of the weasel phrase "My understanding is". As usual, I reserve the right to be proven wrong.

  Thanks Roger.  It would be very interesting to track down the Darwin paper. 

So do I understand correctly: thrum x thrum crosses are impossible while pin x pin crosses are less fertile and can produce only pins?

And in the latter case, is there a decline in vigour?

The chapter on heterostyly and homostyly in John Richard's book addresses this issue in detail, mainly from an evolutionary perspective. 
So if I do understand correctly then the answers to my questions are 'It depends' and 'Yes' respectively.

Thanks for the table & reference Giles.  The data are presented as averages but without knowing the sample size or variation it's impossible to know whether values for particular species really differ or not   What they do suggest is very wide variation between and even within sections.

[Paul T]

I've had seed set both ways on Primula vulgaris in the past, but I don't know exactly what progeny results were.  Certainly the first ever that I did were thrum x thrum as that was all I had.  I in future years did pin x pin and pin x thrum successfully as well.  So none of them were impossible for me.  Of course the first time I tried, raising the seedlings was impossible.... but thankfully I've sorted that out since then.    I know I had pin x pin on the P. veris as well, but don't think I have tried thrum x thrum.

Bear in mind also that this paper by the sound of it was on vulgaris only, and therefore may not reflect other species.  Me, I'd be trying for seed from whatever you have.  More plants and different clones is good, even if they are all the same "sex".  If a hybrid you may also get interesting things (and crossing to itself may show you as well that something you thought was a species was actually a hybrid because the progeny throw back to both parents.

It's all fun!!