T EE 
AMERICAN NATURALIST. 
Vol. V.— MARCH, 1871.— No. 1. 
eces eR DD 
THE POLARITY OF THE COMPASS PLANT.* 
BY W. F. WHITNEY. 
Tue first mention of the so-called ‘ polarity” of the Compass 
Plant, Silphium laciniatum, was made in communications ad- 
dressed to the N tea Institute, by General Benj. Alvord, then 
Brevet Major, U. S. A., in August, 1842, and January, 1843; 
although the fact was well known to many hunters and others, as 
subsequent letters have shown. The truth of his statement hav- 
ing been doubted, General Alvord presented another communica- 
tion at the second meeting of the American Association for the 
Advancement of Science, held at Cambridge, August, 1849, in 
which he confirms his own observations by those of other officers, 
all agreeing in the conclusion that the radical leaves of the plant 
really present their edges north and south, while their faces are 
turned east and west, the leaves on the developed stems of the 
flowering plant, however, taking rather an intermediate position 
between their normal or symmetrical arrangement on the stem and 
their peculiar meridional position. 
General Alvord’s first conjecture, that the leaves might have 
taken up so much iron as to become magnetic, having been neg- 
atived by analysis, he suggested that the resinous matter, of which 
the plant was full, and from which it was sometimes called “ Rosin 
Weed,” might have some agency in producing electrical currents. 
As to its geographical distribution, he stated that it extended 
* Read before the Harvard Natural ery Society, at Cambridge, Dec. 6, 1870. 
FOE NENT 
Entered wosoweinng to Act of Congress, in the year 1871, by the PEABODY ACADEMY OF 
SCIENCE, in the Office of the Libraro f Congress, at Washington. 
AMER. NATURALIST, VOL. V. pi 
