161 Hesiod, _Works and Days_, 448-474; Epictetus, _Dissertationes_, iii. 21. 12. For the autumnal migration and clangour of the cranes as the signal for sowing, see Aristophanes, _Birds_, 711; compare Theognis, 1197 _sqq._ But the Greeks also ploughed in spring (Hesiod, _op. cit._ 462; Xenophon, _Oeconom._ 16); indeed they ploughed thrice in the year (Theophrastus, _Historia Plantarum_, vii. 13. 6). At the approach of autumn the cranes of northern Europe collect about rivers and lakes, and after much trumpeting set out in enormous bands on their southward journey to the tropical regions of Africa and India. In early spring they return northward, and their flocks may be descried passing at a marvellous height overhead or halting to rest in the meadows beside some broad river. The bird emits its trumpet-like note both on the ground and on the wing. See Alfred Newton, _Dictionary of Birds_ (London, 1893-1896), pp. 110 _sq._ 162 Hesiod, _Works and Days_, 383 _sq._, 615-617; Aratus, _Phaenomena_, 254-267; L. Ideler, _Handbuch der mathematischen und technischen Chronologie_ (Berlin, 1825-1826), i. 241 _sq._ According to Pliny (_Nat. Hist._ xviii. 49) wheat, barley, and all other cereals were sown in Greece and Asia from the time of the autumn setting of the Pleiades. This date for ploughing and sowing is confirmed by Hippocrates and other medical writers. See W. Smith’s _Dictionary of Greek and Roman Antiquities_,3 i. 234. Latin writers prescribe the same date for the sowing of wheat. See Virgil, _Georg._ i. 219-226; Columella, _De re rustica_, ii. 8; Pliny, _Nat. Hist._ xviii. 223-226. In Columella’s time the Pleiades, he tells us (_l.c._), set in the morning of October 24th of the Julian calendar, which would correspond to the October 16th of our reckoning. 163 Plutarch, _Isis et Osiris_, 69.