in Thoreau’s Journal:

At Clematis Brook I perceive that the pods or follicles of the Asclepias Syriaca point upward––(did they before all point down?)

They are already bursting. I release some seeds with the long fine silk attached––the fine threads fly apart open with a spring as soon as released––& then ray themselves out into a hemispherical form, each thread freeing itself from its neighbor & all reflecting prismatic tints.

The seeds besides are winged, I let one go and it rises slowly & uncertainly at first now driven this way then that, by airs which I can not perceive––& I fear it will make shipwreck against the neighboring wood––but no, as it approaches it––it surely rises above it & then feeling the strong north wind it is borne off rapidly in the opposite direction––ever rising higher & higher––& tossing & heaved about with every commotion––till at a hundred feet in the air & 50 rods off steering south I loose sight of it. How many myriads go sailing away at this season over hill & meadow & river––to plant their race in new localities––on various tacks until the wind lulls––who can tell how many miles. And for this end these silken streamers have been perfecting all summer, snugly packed in this light chest––a perfect adaptation to this end––a prophecy of the fall & of future openings. Who could believe in the prophecies of Daniel or of Miller that the world would end this summer while one Milkweed with faith matured its seeds!