Thistles and Nettles 325 
thus effectually protected, their upper sides are not 
always left unguarded. About one teasel in three 
has its upper leaf-surfaces dotted over with prickles, 
not very sharp to the fingers, but probably well 
able to hurt the lips and tongue of a browsing 
animal, and these prickles, by the bye, are interest- 
ing to the botanist, because they grow out of the 
leaf-surface, and not, after the usual habit of prick- 
les, from the veins. A hungry rabbit, feeding 
among the teasels, would be likely to satisfy his 
appetite with those leaves having their upper sur- 
faces soft and smooth, and to spare the more 
bristly individuals. So these well-guarded plants 
survive to set their seed, and become progenitors 
of young plants, which will inherit the parental 
habit of bearing leaves with prickles on both sur- 
faces. 
The botanist draws a distinction between a prickle 
and a thorn. A prickle can be removed with ease 
from the stem or leaf on which it grows. It is 
not incorporated with the wood, but merely, and 
often very lightly, attached to the bark or to the 
surface or edge of the leaf. 
A thorn is, on the contrary, a fixture. The 
woody fibre of the plant runs up into it, and it 
cannot be detached without considerable difficulty. 
