It well repays one to observe the relative times of maturing anthers and stigmas in the flowers, as thereby hangs a tale in which some insect plays an interesting role. The figwort matures its stigma at the lip of the style before its anthers have ripened their pollen. Why? By having the stigma of a newly opened flower thrust forward to the mouth of the corolla, an insect alighting on the lip, which forms his only convenient landing place, must brush against it and leave upon it some pollen brought from an older flower, whose anthers are already matured. At this early stage of the flower's development its stamens lie curved over in the tube of the corolla; but presently, as the already fertilized style begins to wither, and its stigma is dry and no longer receptive to pollen, then, since there can be no longer any fear of self-pollination - the horror of so many flowers - the figwort uncurls and elevates its stamens. The insect visitor in search of nectar must get dusted with pollen from the late maturing anthers now ready for him. By this ingenious method the flower becomes cross-fertilized and wastes the least pollen.
Bees and wasps evidently pursue opposite routes in going to work, the former beginning at the bottom of a spike or raceme, where the older, more mature flowers are, and working upward; the wasps commencing at the top, among the newly opened ones. In spite of the fact that we usually see hive bees about this plant, pilfering the generous supply of nectar in each tiny cup, it is undoubtedly the wasp that is the flower's truest benefactor, since he carries pollen from the older blossoms of the last raceme visited to the projecting stigmas of the newly opened flowers at the top of the next cluster. Manifestly no flower, even though it were especially adapted to wasps, as this one is, could exclude bees. About one-third of all its visitors are wasps.
HAIRY BEARD-TONGUE
(Pentstemon hirsutus; P. pubescens of Gray) Figwort family
Flowers - Dull violet or lilac and white, about 1 in. long, borne in a loose spike. Calyx 5-parted, the sharply pointed sepals overlapping; corolla, a gradually inflated tube widening where the mouth divides into a 2-lobed upper lip and a 3-lobed lower lip; the throat nearly closed by hairy palate at base of lower lip; sterile fifth stamen densely bearded for half its length; 4 anther-bearing stamens, the anthers divergent. Stem: 1 to 3 ft. high, erect, downy above. Leaves: Oblong to lance shape, upper ones seated on stem; lower ones narrowed into petioles. Preferred Habitat - Dry or rocky fields, thickets, and open woods. Flowering Season - May-July. Distribution - Ontario to Florida, Manitoba to Texas.
It is the densely bearded, yellow, fifth stamen (pente =five, stemon = a stamen) which gives this flower its scientific name and its chief interest to the structural botanist. From the fact that a blossom has a lip in the center of the lower half of its corolla, that an insect must use as its landing place, comes the necessity for the pistil to occupy a central position. Naturally, a fifth stamen would be only in its way, an encumbrance to be banished in time. In the figwort, for example, we have seen the fifth stamen reduced, from long sterility, to a mere scale on the roof of the corolla tube in other lipped flowers, the useless organ has disappeared; but in the beard-tongue, it goes through a series of curious curves from the upper to the under side of the flower to get out of the way of the pistil. Yet it serves an admirable purpose in helping close the mouth of the flower, which the hairy lip alone could not adequately guard against pilferers. A long-tongued bee, thrusting in his head up to his eyes only, receives the pollen in his face. The blossom is male (staminate) in its first stage and female (pistillate) in its second.
While this is the beard-tongue commonly found in the Eastern United States, particularly southward, and one of the most beautiful of its clan, the western species have been selected by the gardeners for hybridizing into those more showy, but often less charming, flowers now quite extensively cultivated. Several varieties of these, having escaped from gardens in the East, are locally common wild.
The LARGE-FLOWERED BEARD-TONGUE (P. grandiflorus), one of the finest prairie species, whose lavender-blue, bell-shaped corolla is abruptly dilated above the calyx, measures nearly two inches long. Its sterile filament, curved over at the summit, is bearded there only.
Handsomest of all is the COBEA BEARD-TONGUE, a native of the Southwest, with a broadly rounded, bell-shaped corolla, hairy without, like the leaves, but smooth within. The pale purple blossom, delicately suffused with yellow, and pencilled with red lines - pathfinders for the bees - has the base of its tube creamy white. Few flowers hang from each stout clammy spike.
The more densely crowded spikes of the large SMOOTH BEARD-TONGUE (P. glaber), a smaller blue or purple flowered, narrower-leaved species, that shows an unusual preference for moist soil throughout its range, is, like the other beard-tongues mentioned, better known to the British gardener, perhaps, than to Americans, who have yet to learn the value of many of their wild flowers under cultivation.
The tall FOXGLOVE BEARD-TONGUE (P. digitalis), with large, showy white blossoms tinged with purple, the one most commonly grown in gardens here, escapes on the slightest encouragement to run wild again from Maine to Virginia, west to Illinois and Arkansas. Small bees crawl into the broad tube, and butterflies drain the nectar evidently secreted for long-tongued bees, but without certainly transferring pollen. To insure cross-fertilization, the flower first develops its anthers, whose saw-edges grating against the visitors thorax, aid in sifting out the dry pollen; and later the style, which when immature clung to the top of the corolla, lowers its receptive stigma to oppose the bee's entrance. Professor Robertson has frequently detected the common wasp nipping holes with her sharp jaws in the base of the tube. With remarkable intelligence she invariably chose to insert her tongue at the precise spots where the nectar is stored on either side of the sterile filament.