Quem qui scire velit, Libyci velit aequoris idem
Discere quam multae Zephyro turbentur arenae.
(Scire quam multae Zephyro truduntur harenae. says David Womersley)
Ammianus has inserted in his prose these lines of Virgil (Georgic. 1. ii. 105), originally designed by the poet to express the impossibility of numbering the different sorts of vines. See Plin. Hist. Natur. 1. xiv.