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 - Numerous, small, about 1/4 in. across, involucre cyl-indric, rays pale yellow; followed by abundant, soft, bright white pappus; the heads growing in loose, branching, terminal clusters. Stem: Smooth, 3 to 10 ft. high, leafy up to the flower panicle; juice milky. Leaves: Upper ones lance shaped; lower ones often 1 ft. long, wavy-lobed, often pin-natifid, taper pointed, narrowed into flat petioles.
Preferred Habitat - Moist, open ground; roadsides.
Flowering Season - June - November.
Distribution - Georgia, westward to Arkansas, north to the British Possessions.
Few gardeners allow the table lettuce (saliva) to go to seed; but as it is next of kin to this common wayside weed, it bears a strong likeness to it in the loose, narrow panicles of cream-colored flowers, followed by more charming, bright white little pompons. Where the garden varieties originated, or what they were, nobody knows. Herodotus says lettuce was eaten as a salad in 550 B.C.; in Pliny's time it was cultivated, and even blanched, so as to be had at all seasons of the year by the Romans. Among the privy-purse expenses of Henry VIII. is a reward to a certain gardener for bringing "lettuze" and cherries to Hampton Court. Quaint old Parkinson, enumerating "the vertues of the Iettice," says, "They all cool a hot and fainting stomache." When the milky juice has been thickened (lactucarium), it is sometimes used as a substitute for opium by regular practitioners - a fluid employed by the plants themselves, it is thought, to discourage creatures from feasting at their expense (see milkweed, p. 137). Certain caterpillars, however, eat the leaves readily; but offer lettuce or poppy foliage to grazing cattle, and they will go without food rather than touch it.
" What's one man's poison, Signor, Is another's meat or drink."
Rabbits, for example, have been fed on the deadly nightshade for a week without injury.
The Hairy or Red Wild Lettuce (L. hirsnta), similar to the preceding, but often with dark reddish stem, peduncles, and tiny flower-cups, the ray florets varying from yellow to pale reddish or purplish, has longer leaves, deeply cut or lobed almost to the wide midrib. After what we learned when studying the barberry and the prickly pear cactus, for example, about plants that choose to live in dry soil, it is not surprising to find that this is a lower, less leafy, and more hairy plant than the moisture-loving tall lettuce.
An European immigrant, naturalized here but recently, the Prickly Lettuce (L. Scariola) has nevertheless made itself so very much at home in a short time that it has already become a troublesome weed from New England to Pennsylvania, westward to Minnesota and Missouri. But when we calculate that every plant produces over eight thousand fluffy white-winged seeds on its narrow panicle, ready to sail away on the first breeze, no wonder so well endowed and prolific an invader marches triumphantly across continents. The long, pale green, spiny-margined, milky leaves, with stiff prickles on the midrib beneath, are doubly protected against insect borers and grazing cattle.
"Look at this delicate plant that lifts its head from the meadow; See how its leaves all point to the North as true as the magnet."
While Longfellow must have had the coarse-growing, yellow-flowered, daisy-like prairie rosin-weed (Silphium laciniatum) in mind when he wrote this stanza of "Evangeline," his lines apply with more exactness to the delicate prickly lettuce, our eastern compass plant. Not until 1895 did Professor J. C. Arthur discover that when the garden lettuce is allowed to flower, its stem leaves also exhibit polarity. The great lower leaves of the rosin-weed, which stand nearly vertical, with their faces to the east and west, and their edges to the north and south, have directed many a traveller, not from Acadia only, across the prairie until it has earned the titles pilot-weed, compass or polar plant. Various theories have been advanced to account for the curious phenomenon, some claiming that the leaves contained sufficient iron to reader them magnetic - a theory promptly exploded by chemical analysis.' Others supposed that the resinous character of the leaves made them susceptible to magnetic influence; but as rosin is a non-conductor of electricity, of course this hypothesis likewise proved untenable. At last Dr. Asa Gray brought forward the only sensible explanation: inasmuch as both surfaces of the rosin-weed leaf are essentially alike, there being very nearly as many stomata on the upper side as on the under, both surfaces are equally sensitive to sunlight; therefore the leaf twists on its petiole until both sides share it as equally as is possible. While the polarity of the prickly lettuce leaves is by no means so marked, Dr. Gray's theory about the rosin-weed may be applied to them as well.