Layout.

From this layout, you can recognize the closure and proximity. Two symbols make the audience understand which one represents to male and which one for female. They overlap together (they are having sex). Just look at this symbol (having two flowers inside) we can know what this layout want to say. Furthermore, the text “The secret sex of plants” is put into the blue area; it makes the audience pay attention to easily. Moreover, both text and these symbols are put in the light colour area to separate to the body text.