DAYLILY FERTILIZATIONOne often reads in catalog descriptions terms such as "fertile both way" and "pollen hot but will not set pods."
What underlying phenomena underlies those attributes? It is called pollen compatibility. The stigma, that sticky tip of the pistil that receives the pollen grains, doesn't let every pollen grain in, it is selective. For instance, it will react to pollen from a flower of another species (for example, the pollen of a neighboring hosta) by producing substances that inhibit the growth of these pollen grains down the pistil to fertilize the ovules within. Some species even recognize their own pollen to avoid self-fertilization. Hemerocallis is among such species, though self-compatibility occasionally does occur. Pollen from plants that are closely related to each other may be mistaken as 'self' and prevented to reaching the ovules.
In addition to issues of self-incompatibility, or pollen grains that are too closely related, there is the issue of actual sterility. A plant may have fertile pollen, but carry a mutation that prevents it from producing viable seeds. The production and release of pollen grains requires the action of fewer genes than the recognition of appropriate pollen grains, the helping the pollen grain along the pollen tube, and the production of a seed following fertilization. Because there are fewer genes involved in the male side of things as opposed to the female side, the chances of having a mutated gene disabling some aspect of pollen function is quite a bit smaller than the chances of something going wrong with a gene required for seed production in the pod parent.
That's why there are more plants that have difficulty setting pods than having infertile pollen. There's more to it, more can go wrong.