Which of the following substances is NOT typically secreted by secretory cells?

The chosen answer, flowers, is correct because flowers themselves are not substances secreted by secretory cells. Instead, flowers are structures of the plant that contain reproductive organs, including petals, sepals, stamens, and carpels.

On the other hand, nectar, glandular hair mucilage, and resins are all products of secretory cells. Nectar, produced in nectarines, serves to attract pollinators by providing them with a sugary reward. Glandular hair mucilage, which can be secreted by specific hair-like structures on some plants, aids in various functions such as trapping insects or providing a protective coating. Resins, produced by specific plants, serve various purposes including wound sealing and deterring herbivory. Therefore, these substances are all examples of secretions from secretory cells that fulfill important ecological roles.