A while ago I posted a picture of a seed of Maihuenia patagonica germinating after being treated with GA-3. Well, it turns out that either I used too much GA-3, or treating this species results in seedling elongation.
I haven’t had this problem with anything else I’ve treated, but in this case I think the situation is hopeless. Yes, this is a cactus.
There is one seed germinating beside it; I decided to nick the seed, which is pretty large (visible in the picture), using my handy extra-sharp Opinel. One seed went down my pants (I don’t know how, it just did) and when I shook it out, I stepped on it and smashed it. One flew out of my fingers and an after an hour of crawling around the kitchen floor I gave up looking for it, but four or five have been nicked, and the results are very promising.
The germinating seed is just the the left of the bend in the hugely elongated stem of the seed which germinated earlier, but here it is up close, though not in focus. 
the miserable gardener 
Bob,
M. patagonica seems to naturally elongate, whether or not treated with GA. I carefully repot the seedlings (after a few weeks) and that works most of the time. I have better luck with old seed;
last fall I germinated some seed that I collected 25 years ago.
Do you cellar it, like wine? I’ve heard that older seed works well, but this gardener is getting older, too. ….
Echinocactus horizonthalonius seems to elongate with GA3. I have nothing with which to compare since I’ve never been able to germinate the seed. Until now. Ditto E. xeranthemoides.
Again, old seed is best. I collected seed of E. xeranthemoides this past August at one of its highest known localities (~5200′) and will be glad to give you some to try. E. horizonthalonius is extremely difficult in the garden as young plants. I gave up after several attemps with both seed-grown and collected plants and now keep a large one in my greenhouse and keep it outside all spring ad summer for the fabulous large and very sudden purple flower–from invisible bud to fully open flower in 24 flowers!
Okay. I saw some big horizonthalonius for sale online somewhere, 20 or 40 bucks each. My experience has been the same, little ones turn white and die. I bet they don’t experience six month long winters in their homeland.
I bet Chess enjoyed that episode of seed searching. Or slept through it.
Probably. The maihuenia grown under lights didn’t survive, but the ones germinated outdoors did. I gave them away, though, because I already had plants.