Our Fathers of Old' Excellent herbs had our fathers of old--
Excellent herbs to ease their pain--
Alexanders and Marigold,
Eyebright, Orris, and Elecampane
, Basil, Rocket, Valerian, Rue,
(Almost singing themselves they run)
Vervain, Dittany, Call-me-to-you--
Cowslip, Melilot, Rose of the Sun.
This is 'Our Fathers of Old' by Kipling.
I can not understand the meaning of the sentence below.
Almost singing themselves they run
I am glad if somebody kindly teach me.