This section is from the book "Nature's Garden", by Neltje Blanchan. Also available from Amazon: Nature's Garden; An Aid To Knowledge Of Our Wild Flowers And Their Insect Visitors.
Flower-heads - Yellow, nearly flat, 2 to 3 in. across; 20 to 30 narrow, pistillate ray florets, about 1 in. long, overlapping in 2 or 3 series around the perfect but sterile disk florets. Stem: 4 to 8 ft. tall, square, smooth, usually branched above. Leaves: Opposite, ovate, upper ones united by their bases to form a cup; lower ones large, coarsely toothed, and narrowed into margined petioles; all filled with resinous juice.
Preferred Habitat - Moist soil, low ground near streams.
Floivering Season - July - September.
Distribution - Ontario, New York, and Georgia, westward to Minnesota, Nebraska, and Louisiana.
It behooves a species related to the wonderful compass-plant (see p. 346) to do something unusual with its leaves; hence this one makes cups to catch rain by uniting its upper pairs. Darwin's experiments with infinitesimal doses of ammonia in stimulating leaf activity may throw some light on this singular arrangement. So many plants provide traps to catch rain, although fourteen gallons of it contain only one grain of ammonia, that we must believe there is a wise physiological reason for calling upon the leaves to assist the roots in absorbing it. A native of Western prairies, the cup-plant has now become naturalized so far east as the neighborhood of New York City.