THE 
AMERICAN NATURALIST. 
VoL. xu.— OCTOBER, 1878. — No. to. 
HOW THISTLES SPIN. 
BY PROF. W. J. BEAL. 3 
HASTY glance at a plant of Cirsium. altissimum, a very tall 
thistle, shows that the main stem, its branches, the midrib 
and prominent veins of the leaf are clothed with soft slender 
hairs. The entire under surface of the leaf is white or gray with 
~ a dense coat of cotton. The scales of the spiny-tipped involucre 
appear as if they were tied together by numerous gossamer 
threads. If the young leaves and buds are pulled apart many 
fine threads spin out an inch or more until the parts are separated 
far enough to break the threads. 
Under a magnifying power of one hundred iene. the 
larger hairs, an eighth of an inch in length, are seen to be com- 
posed of a row of about fifteen 
cells placed end to end. he 
largest hairs are found on the | 
stems and midribs. 
At the top of the jointed hairsis 
a long lash, sometimes an inch in 
length which generally extends 
_ towards the tip of the leaf or stem. 
These hairs are very numerous, 
and stick more or less to each 
other. Fig. 1 isa good represen- 
tation of one of these hairs while 
young, before it has been drawn 
out at the extremity. Fig. 2 rep- ; 
resents a similar hair more highly Seis 
Magnified. In the latter case oe a of Cirsium a al- 
Ol 
up to form the thread-like lash at the PA: 
VOL. XII —No. x, 44 
