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 - Purple, violet, or lilac, rarely whitish; about 1 in. long, solitary, borne on slender footstems from axils of upper leaves. Calyx prismatic, 5-angled, 5-toothed; corolla irregular, tubular, narrow in throat, 2-lipped; upper lip 2-lobed, erect; under lip 3-lobed, spreading; 4 stamens, a long and a short pair, inserted on corolla tube; 1 pistil with 2-lobed, plate-like stigma. Stem: Square, erect, usually branched, 1 to 3 ft. high. Leaves: Opposite, oblong to lance-shaped, saw-edged, mostly seated on stem. Preferred Habitat - Swamps, beside streams and ponds. Flowering Season - June - September. Distribution - Manitoba, Nebraska, and Texas, eastward to Atlantic Ocean.
Monkey-Flower. (Mimulus ringens.)
No wader is the square-stemmed Monkey-flower whose grinning corolla peers at one from grassy tuffets in swamps, from the brookside, the springy soil of low meadows, and damp hollows beside the road; but moisture it must have to fill its nectary and to soften the ground for the easier transit of its creeping rootstock. Imaginative eyes see what appears to them the gaping (ringens) face of a little ape or buffoon (mimulus) in this common flower whose drolleries, such as they are, call forth the only applause desired - the buzz of insects that become pollen-laden during the entertainment.
Now the advanced stigma of this flower is peculiarly irritable, and closes up on contact with an incoming visitor's body, thus exposing the pollen-laden anthers behind it, and, except in rare cases, preventing self-fertilization. Delpino was the first to guess what advantage so sensitive a stigma might mean. Probably the smaller bees find the tube too long for their short tongues. The yellow palate, which partially guards the entrance to the nectary from pilferers, of course serves also as a pathfinder to the long-tongued bees.