Ammianus Marcellinus Res Gestae 24.3.13

[13] It is also said that the female trees conceive when smeared with the seeds of the male, and they assert that the trees take pleasure in mutual love, and that this is evident from the fact that they lean towards each other, and cannot be parted even by gales of wind. And if the female tree is not smeared in the usual way with the seed of the male, it suffers abortion and loses its fruit before it is ripe. And if it is not known with what male any female tree is in love, her trunk is smeared with her own perfume, ¹ and the other tree by a law of nature is attracted by the sweet odour. ² It is from these signs that the belief in a kind of copulation is created.