I assume these are pelargorum

I have never tried to collect seed but I know some hybrids make seeds. I break my spent blooms off so they will make more flowers. Collecting seeds from any hybrid will not get you a plant like the one you took the seed from. It can resemble any one of it's ancestors or be a mixture of any of them

I make more plants by taking cuttings like you are doing or buy seed. Many growers take cuttings too. You can have a blooming plant in a couple of months from a cutting as opposed to 4 months from seed

If you purchase seed it will be no different than the plants you buy unless you can find somewhere that sells heirloom geraniums--if there is such a place

I have hybrids that give seeds and other not. This depends of the chromosomes'pairs in the hybridization. I like to buy Maverick seeds and Orbit seeds because I enjoy seeing them grow and develop. Park Seeds y Garden Harvest Supply have good seeds.

To exclude lack of pollinators, you may try hand pollination. However, some hybrids will make lots of flowers and still fail to pollinate. There reason is in the chromosomes as Maritza said: A normal plant is diploid, i.e. has one pair of each chromosome: One chromosome from the ovule and one from the pollen, giving two of each. (The pollen and the ovule are haploid, having a single chromosome of each. Only upon fertilization, the lone chromosomes pair-up in the fertilized ovule).

Some chemicals, such as Colchicine, disrupt the cell division and result in doubling the number of chromosomes in the plant cells. Quote from Wikipedia: "Colchicine is also used for inducing polyploidy in plant cells during cellular division by inhibiting chromosome segregation during meiosis"

A plant cell exposed to colchicine does not segregate the chromosomes and the cell ends-up with a double number. The resulting plant is tetraploid, having 2 pairs of each chromosome, or 4 of each. The tetraploid is fertile, but when crossed with a diploid, the resulting seed will give a triploid plant, having 3 chromosomes of each. An odd number means that when chromosomes group in pairs, one will remain solitary. The reason is as follows: One of the cells (ovule, or pollen) is diploid (2n), the other is haploid (n). The fertilized egg will be triploid (2n+n=3n).

The triploid plant will flower profusely, but will fail to fertilize. Even a thorough hand pollination will give you no seeds at all. This is how seedless fruits are developed. https://en.wikipedia.org/wiki/Seedless_fruit

Hi! Asclepiad:

I knew that because I have many triploids in my garden and I had to stady hybridization to know why did not they give me seeds. Your exposure of the subject is very nice and explicit, l congratulate you, greetings.