The principles of botany, and of vegetable physiology pp. 322-323 (1805)
Karl Ludwig Willdenow

291.

Koelreuter examined, in a very laborious manner, how many globules of pollen might be required to complete an impregnation. His chief discoveries on this point are as follow:

All the anthers of Hibiscus syriacus contained 4863 globules of pollen, 50 or 60 of which were necessary to complete impregnation. But whenever he took less than 50 globules, then not all the seeds ripened, but those, which were formed, were perfect. Ten globules were the least he could take in this flower, as less would not suffice for it.

Hibiscus syriacus biblio