Now, let us suppose that the juice or nectar was excreted from the inside of the flowers of a certain number of plants of any species.

Insects in seeking the nectar would get dusted with pollen, and would often transport it from one flower to another.

The flowers of two distinct individuals of the same species would thus get crossed; and the act of crossing, as can be fully proved, gives rise to vigorous seedlings, which consequently would have the best chance of flourishing and surviving.