CELLS. STINGS. 
69 
in a transverse section of the shell of a Cocoa-nut are 
seen; and in Fig. 55, a horizontal section of the same 
shell, not only the thickened cells are shown, but close 
to them a part of a bundle of peculiar vessels, somewhat 
like those occurring in Ferns. 
Spiral vessels are occasionally met with both in the 
shells of the Walnut and Hazel-nut. 
In addition to the substances already described as 
examples of the more common contents of cells, a few of 
a peculiar nature demand some notice. 
Certain plants are provided with offensive weapons, 
some of which are known as stings, being (as in the 
Nettle) elongated cells or hairs developed from the 
cuticle, and usually of a conical figure. They contain a 
poisonous or irritating fluid, in which, in some cases, 
a cyclosis or circulation is visible. When examined 
with a power of one hundred diameters, as represented 
by a , b , in Fig. 56, each sting is seen to have either 
a minute bulbous or triangu- 
lar free extremity attached by 
a narrow neck to the apex of 
the shaft ; the part connected 
with the cuticle is much ex- 
panded, and around its base 
are certain more or less poly- 
gonal cuticular cells. The 
contents of the hair are al- 
ways in a state of tension, 
and when the hand is passed 
fig. 56 . 
'J 
a, b, stinging hairs of the Net- 
tle ( Urtica dioicci ) ; c, d, e, ciliated 
spores of Confervas. 
