233
NOTES ON THE TEASELS, DIPSACUS SYLVES-
TRIS AND D. PILOSUS, AND THEIR
NATURAL RELATIONSHIP.
By J. FRENCH.
[Read December 2nd, 1890.]
THE Teasel, Dipsacus sylvestris, in its stage of flowering and
seed is so familiar that description is quite unnecessary. Dip-
sacus pilosus, with a more modest appearance, is less common, and
not nearly so well known. Its heads of flowers are nearly globular,
and not half the size of those of its kinsman, and the bloom is white
and inconspicuous. The plant, moreover, is nearly destitute of that
formidable array of prickles so characteristic of D. sylvestris. The
curious arrangement of water-cups in the latter plant, which are
developed at the axils of the leaves at an early stage of its growth, is
absent in D. pilosus. In point of foliage and habit the two plants are
not greatly unlike.
We will now call attention to the prickly apparatus and cups of
D. sylvestris. Neither of these appliances are brought into operation
until the stems1 are in process of development. The cups precede
the prickles, which latter do not appear on the stem until the fourth or
fifth node is reached. The cups, however, cease just before the time
of flowering, while the prickles are hardened and multiplied to a
much later date.
A very cursory examination will assure us that the cup is the
result of a special process, and is not the accidental result of con-
tiguity of leaf bases like Blackstonia, Lonicera, and others. Long
before the leaf attains its full development the puckering at the base
is well marked, and a set of vascular vessels specially contributing
to the support of the cup make their appearance. The rim of the
cup, too, is very entire, and never crenated like the leaf limb. The
cups are absolutely water-tight, only losing water by evaporation and
rupture.
The arrangement of the prickles is such as to indicate a special
design. This design is more pronounced as the plant advances to
seed, and in the species known as the "Fuller's Teasel" (D. fullonum)
it attains its maximum. The points of the prickles are directed down-
wards, as though to repel a foe creeping upwards. In the "Fullers
1 The plants arc, it should be recollected, biennial, and in the first year make only radical
leaves.
Q