76 A TEXTBOOK OF GENERAL BOTANY 
Bristlelike hairs. A number of plants possess stiff, sharp- 
pointed, bristlelike hairs which readily penetrate the skin of man 
* and produce very disagreeable effects. Some of these hairs have 

Fig. 64. Glandular hairs 
Left, water hyacinth; second 
figure, squash ; third figure, to- 
mato ; right, tobacco. (x 200) 
barblike protuberances along their 
sides (Fig. 62). These protuber- 
ances increase the irritating effect 
of the trichomes. Bristlelike hairs 
may afford protection to plants by 
keeping animals from eating the 
leaves, but comparatively few plants 
have hairs stiff enough to be very 
effective in this way. 
Stinging hairs. Stinging hairs are 
one of the most interesting types of 
trichomes (Fig. 63). A typical sting- 
ing hair contains a poisonous liquid 
and consists of a basal bulb-shaped 
portion from which projects a stiff, 
slender, tapering structure that ends 
in a small knob or a sharp point. 
Near the tip there is usually an 
oblique thin place in the wall, so 
that when the body of an animal or 
some other object is pressed against 
the tip with sufficient force, the tip 
is broken off, leaving a sharp point 
that can readily penetrate an ani- 
mal’s skin. The wall of the rounded 
basal portion is distended by the 
pressure of the contained liquid, 
and it contracts when this pressure is removed by the breaking 
of the tip. This contraction tends to force the fluid through the 
opening in the tip, so that an animal into which the sharp point 
has stuck will be injected with the poisonous fluid. The pres- 
sure of the animal against the hair also helps to force the liquid 
from the bulbous base. 

