Biological science of our day takes it for granted that the process uniting pollen with seed in the plant is an act of fertilization analogous to that which occurs among the higher organisms of nature. Now it is not to be gainsaid that to external observation this comparison seems obvious, and that it is therefore only natural to speak of the pollen as the male, and of the ovule as the female, element, and of their union as entirely parallel to that between the sexes in the higher kingdoms of nature.