Almost always "seedless seeds" are triploids, which are an F1 hybrid between a diploid strain and a tetraploid strain. As far as I know, no triploid can set viable seed. Seedless watermelons and bananas are more familiar triploids.

MM

So they are selling a bogus product??? Or will it simply not come true?

Neither. Lets say Plant A is diploid or XX Plant be is tetraploid or XXXX. When they cross and they can because each has an even number of chromosomes, the resultant seed is Plant C or XXX. So this is the seed you buy. It's not bogus. But, if you plant the seed for Plant C it will carry the XXX and cannot cross with any other to produce viable seeds. That's why the "seedless" watermelons have tiny immature seeds. The plant it produces is for all purposes sterile. So, there isn't any coming true about it, it simply cannot be bred.

Calliope,

Thanks for the followup explanation. Good details.

MM

You'll notice that the default number of chromosomes is an even number....divisible by two. The reason being, is that in sexual propagation, the sexual cells themselves, since it takes one set from the male and one from the female are just half the chromosomal number of each parent. That's why, when they combine, the form offspring of the proper chromosomal number like the parent. Triploids, and those other hybrids with odd number of chromosomes are often sterile because how can you divide in half an odd number chromosome? It happens sometimes when you push the envelope on cross-breeding members of similar species just a little too distantly related like horses and jackasses and get mules, who are usually, but not always sterile especially hinnies.

Ok, I get the math part, but still don't get the part about reproduction:

If mules are sterile, how do we get more mules? (and seedless watermelons, and seedless grapes, etc)

Likewise, if a plant is sterile (this marigold), then what good are these seeds that are being sold? Where did these seeds come from???

"If mules are sterile, how do we get more mules? (and seedless watermelons, and seedless grapes, etc) "

Same way we got the mule in the first place ... we once again breed a horse to a donkey. Such matings produce children but no grandchildren. [Accept in VERY rare cases as Calliope pointed out.]

"Likewise, if a plant is sterile (this marigold), then what good are these seeds that are being sold? Where did these seeds come from???"

The seeds you are buying are the "children" of parent XX mated with parent XXXX. Remember what Calliope said ... that cross means that these "children"/seeds are XXX -- they have an odd # of chromosomes. They will grow and flower but will not be able to produce offspring of their own because their chromosome # is so screwed up. So again no "grandchildren" for the original parents.

The "value" is generally for the seed company. They are simply warning you that you won't be getting any viable seed from those flowers.

There is also the benefit of knowing that the plant in question won't "make a nuisance of itself" by reseeding

So to sum things up, in order to get seeds for the 'Sunburst' marigold, every year, the seed company has to pollinate 'Susie' marigold flowers with 'Sammy' marigold pollen, just like you pretty much always have to breed a donkey with a horse in order to get a mule.

That's right....and that's why the seeds are so expensive.
Linda C

(light bulb moment) I GET IT!!!

So I gotta go buy these seeds every year. Not thrilled about that, but I get it, I get it!!!

:D