26 THE NATURE-STUDY OF PLANTS 
own would very soon be in jeopardy and on the high 
road to extinction. 
There are, therefore, as we might expect, many 
different ways in which plants are protected against 
being eaten off the face of the earth: they stand, as 
it were, for ever on the defensive, and it is most impor- 
tant to remember that their weapons are of this nature 
and not those of offence. 
With the exception of the few that are insecti- 
vorous they do not attack, but they defend themselves 
with sufficient success against being attacked. In 
this connection the bark, of course, is of great value. 
Although it supports a certain amount of small life 
that may open a door to disease-germs, it offers no 
temptation to most animals and it makes it hard for 
them to reach the succulent cells within. A few 
caterpillars have, however, got the better of it, and 
those of the Goat Moth, with their powerful jaws and 
detestable smell, bore right through it and devour the 
living tissues and other parts within. 
Internal feeders of one sort or another are suffici- 
ently numerous and well known to naturalists, but 
nevertheless bark, whether the thick covering of a 
tree trunk or the thin one of a shrub or bush, prevents 
a very great deal more disaster than the comparatively 
small amount against which it is powerless. 
The hairs which I have already mentioned are 
useful for warding off the attacks of grubs and cater- 
pillars and such horrible things as greenfly and the 
germs or spores of some of the worst diseases from 
which plants suffer, such as rust, smut and mildew. 
There are too, other kinds of hairs to be found in the 
vegetable world, which are not dry and dead like those 
of the Mullein and the Silverweed, but quite the reverse. 
