Watertown republican. [volume] (Watertown, Wis.) 1860-1906, 1877-03-21
THE COMPASS PLANT.
IA Not"rai Guido for Prairie Traysleys-
riot Weed Of the Southwest
From Matt

1t has long been known that there
grows on the prairie lands of the south
western part of the United States of
America, especially Texas and Oregon
plant which has the peculiar pronertv
OF turning It's leaves toward the north,
and which hence serves as q magnet tn
the traveller when no other means is
available of ascertaining the points of
the compass 1t is probable, however.
from Longfellow's description of it IS
delicate plant" on fragile stalk"
that he never saw it growing. The
compass plant is O. member of the
enormous natural order Of composite.
known to botanists as silphium lacinia-
tum. It is described as q slut peren-
lal plant from three to six feet height,
with ovate, deeply pinnatifed leaves
and large yellow heads Of unisexual
flowers, the rayhorets strap-shaped and
female, the disc-forets tabular and
male. 1t is also known as the pilot
weed, polar plant, resin weed and tur-
pentine weed, the last two names being
derived from from the abundant resin
exuded by the stem, and Ia occasionally
to be seen in English gardens. The
polarity" of the leaves of this singu-
lar plant has been familiar to hunters
and other denizens of the praisie, who
when lost on the prairies in dark
nights, easily get their bearings
by feeling the direction of
the leaves" But the first oc-
casion On which it wss brought
under the notice of scientific men ap-
pears to have been in communications
addressed to the National Institute at
Washington in August, 1912, and
January 1843, by General Alvord.
The accuracy of his statement having
been questioned, the General presented
another communication at the second
meeting of the American Association
for the Advancement Of Science, held
at Cam bridge, Mass, IN August 1849,
IN which he confirms his own observa-
tons by those of other officers, all
agreeing IN the conclusion that the
radical leaves Of the plant really pre-
sent their edges north and south, while
their faces are turned east and west.
the leaves on the developed stem of
the lowering plant, however, taking
rather al intermediate position be-
tween their normal or symmetrical ar
rangement Of their peculiar meridianal
position. For the following particulars
respecting the phenomena exhibited
by the compass plant We are indebted
mainly to q paper by Mr.. W. F.
Whitney, read before the Natural His.
tory Society and printed in the Amer
lean Naturalist, and to some subse-
quent notes by Professor Asa and Mr..
Thomas Meehan. The cause of the
ordinary position of the leaves of
most plants, one surface being directed
toward the sky, and the other toward
the earth, is generally believed to be
difference in the sensitiveness to
light of the two surfaces, the epider-
NAL tissue OF the upper being generally
denser and less pervious to light than
that of the under surface. It is pos
slble also that something may be due
to the fact that the under surface
of the leaf is almost always
more copiously furnished with
stomates Or breathing pores" as they
are often inaccurately termed, minute
orihces which serve to promote diff
fusion of gas between the external air
and the intercellular cavities within the
| tissue, and especially al abundant ex-
halation of aqueous vapor. 4 micro
scopical examination of the leaves of
the compass plant shows That the struc-
ture of the epidermal tissue of the two
surfaces is similar, and also that the
number Of stomates in each CORES
ponds, afordlng in this respect q con-
trast to other allied species Of the
genius SiEphia1na, which do not exhibit
the phenomenon of polarity, and in
whose leaves the stomates were found
| to be from two to thee times as nu-
merOus on the under as On the upper
surface. If, therefore, the object to
be gained Is an equal sensitiveness to
light, it is obvious that the two surfaces
will receive an equal amount Of light
during the tWenty-four hours, if they
face the east and the west, rather than
If they face the north and the south or
the earth and the sky. An attempt
has also been made to explain the phe-
nomenon of polarity by currents of
electricity induced by the peculiar
chemical composition Of the substances
secreted by the stem and the leaves,
but not with much success. In recent
communication to the Academy of Nat
ural Science at Philadelphia, Mr..
Meehan says that those who affirm that
the leaves are directed TO the north,
and those who say that there is no such
tendency, are both right. He watch
ed a plant in his own garden, and OBJ
served the unmistakable northern ten
dency in the leaves when they first
came up, and until they were
large and heavy, when winds and
rain bore them in different directions
and they evidently had not the power
of regaining the points lost. Il would
appear, therefore, to depend on the
season when the observation is made
whether the leaves are seen to bear
northward Or not. The same observer
records also the following facts with re-
gard to the flowers of the compass
plant. The expansion Of the ray fiorets
in August was observed to begin at
daybreak, 4 A. NJ; forty minutes after
wards the forets of the disk began to
open, and the whole of the corollas
were expanded in about three. quarters
of an hour, after which there was no
further growth in the corollas. The
orr ~, IL