644 How Thistles Spin. [ October, 
In Fig. 1 the hair appears not to have acquired its growth. 
Near the base the cells are still very short, and not as they appear 
at the base of figure two. Some of the upper cells are slightly 
darker, and are filled with a yellowish-white mucilage. When 
young, the extreme cells are long, smooth and tapering. At that 
time they lie flat on each other, and are sticky and adhere to the 
tips of the hairs which they overlap. As the leaf or stem grows 
in length, the hair-stalks straighten up, and from the tip of each 
a thread is drawn out. In this process some of the cells are 
exhausted and used up in the thread. 
When the flower-bud is an eighth of an inch in diameter and 
one of the surrounding scales the twentieth of an inch in width, 
some of the hairs on the margin of the scale appear like Fig. 3, 
where one short cell is tipped with another— - 
long and slender. These tips are sticky and 
Fiaa may be easily drawn out. As the buds 
Margin young scale expand, the tips of these hairs are caught 
wi Soma and drawn to the right or left by the scales 
next to them. When full grown the heads look as though a 
spider had spun webs round and round the outside. At this time 
SESS the hairs appear like Figs. 4 
D and 5, where there is a long : 
lash with one or two or rarely 
more cells at the base. Fig. 
6-shows the edge of a scale of 
the involucre with one of 
Hairs on the back of a full-grown leaf. 
these hairs, the part of another, and a couple of short prickles. 
_ The webby layer of white or gray on the under side of the 
leaf is composed of cells similar to those last mentioned. They 
appear to grow ina similar manner. As the young leaf spreads 
= and elongates, each hair draws out a thread which helps to cover 
: the under surface with a dense web. This web adheres quite i 5 
closely and firmly to the surface of the leaf. 
