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.
Flowers - Light yellowish, lemon-scented, about 1/2 in. long, mostly opposite, in numerous spreading racemes, forming long, loose, terminal clusters. Calyx bell-shaped, 2-lipped, upper lip 3toothed, lower lip 2-cleft; corolla 5-lobed, 4 lobes nearly equal, the fifth much larger, fringed; stamens protruding, 2 anther-bearing; 1 long style, the stigma forked.
Preferred Habitat - Rich, moist woods.
Flowering Season - July - October.
Distribution - New England, Ontario, and Wisconsin, south to Florida and Kansas.
Now that we have come to read the faces of flowers much as their insect friends must have done for countless ages, we suspect at a glance that the strong-scented horse-balm, with its profusion of lemon-colored, irregular little blossoms, is up to some ingenious trick. The lower lip, out of all proportion to the rest of the corolla, flaunting its enticing fringes; the long stamens protruding from some flowers, and only the long style from others on the same plant, excite our curiosity. Where many fragrant clumps grow in cool, shady woods at midsummer, is an excellent place to rest a while and satisfy it. Presently a bumblebee, attracted by the odor from afar, alights on the fringed platform too weak to hold him. Dropping downward, he snatches the filaments of the two long stamens to save himself; and, as he does so, pollen jarred out of their anther sacs falls on his thorax at the juncture of his wings. Hanging beneath the flower a second, he sips its nectar and is off. Many bees, large and small, go through a similar performance. Now the young, newly opened flowers have the forked stigmas of the long style only protruding at this stage, the miniature stamens being still curled within the tube. Obviously a pollen-dusted bee coming to one of these young flowers must rub off some of the vitalizing dust on the sticky fork that purposely impedes his entrance at the precise spot necessary. Notice that after a flower's stamens protrude in the second stage of its development the fork is turned far to one side to get out of harm's way - self-fertilization being an abomination. It was the lamented William Hamilton Gibson who first called attention to the horse-balm's ingenious scheme to prevent it.