Note 880 — BOOK XIX. THE NATURE AND CULTIVATION OF FLAX, AND AN ACCOUNT OF VARIOUS GARDEN PLANTS.
John Bostock translation
It is really propagated by spores, included in sinuous chambers in the interior; but, notwithstanding the attempts that have been made, it has never yet been cultivated with any degree of success. In c. 13, Pliny seems to recognize the possibility of its multiplication by germs, where he says that its formation is attributed by some to water.