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 traveler, 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.
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