PRICKLES, THORNS, ETC. 33 
with a glass, are found to be formed in different ways; 
sometimes they consist only of a single cavity, or cell 
(pl. 12. f. 3 a. 6.); while others are made up of two 
or three cavities or cells, joined end to end (f.8 ¢. d.). 
In the Mallow, or Hollyhock, several hairs are iaoad 
together, round a common point or centre, so as to 
have the appearance of a star (f. 3. ¢.). In the common 
Nettle the hair is a single tube, with a swelling below 
where it joins the leaf (f. 4.); the tube contains an 
irritating fluid, which causes the burning sensation 
called stinging by a nettle; the point of the hair 
breaks off in the skin, and the fluid is discharged, so 
that there is a double cause for the pain produced. 
36. Some Leaves, as those of the Sweet Briar, are 
furnished with what are called glands, these are small 
round bodies placed on a short stem or stalk, and 
contain a scented fluid (f. 3. g.); in other plants glands 
are placed either upon the surface of the leaf without 
any stalk; or, as in the Orange, and Myrtle, they are 
in the leat itself, and may be seen by holding it up to 
the light, when they will appear as fine transparent 
dots 
On the Leaves and Stem of the Rose, Sweet Briar, 
and other plants, are found what are commonly and 
wrongly called thorns; they are properly speaking 
prickles (pl. 3. f. 1. .), and can be pulled off as they are 
merely fixed to the surface on which they are placed : 
they appear to be hairs in a thickened, and hardened 
state. 
The true thorn is to be seen in the Sloe Tree (pl. 4. 
f, 4.); this is, in reality, a branch which bears only 
2 D 
