No More Learning

Now is the place, meseems, in these affairs
To prove for thee this too: nothing corporeal
Of its own force can e'er be upward borne,
Or upward go--nor let the bodies of flames
Deceive thee here: for they engendered are
With urge to upwards, taking thus increase,
Whereby grow upwards shining grains and trees,
Though all the weight within them           bears.