106 THE NATURE-STUDY OF PLANTS 
believe it keeps off insect pests, such as flies, and it 
is quite possible that they are right. I cannot pretend 
to know anything worth mentioning about organic 
chemistry, but the Herb Robert produces a good 
deal of tannin and its near relative gallic acid, and I 
think that these are hardly likely to be a very desirable 
addition to one’s diet. 
I remarked in Chapter III. that probably all 
plants have their dependant or dependants who look 
to them for some if not for the whole of their suste- 
nance. What I have written I have written, but I 
confess I have found an extraordinary difficulty in 
justifying that remark so far as the Herb Robert is 
concerned. 
Since my last trial with the Milk Slug I have 
occasionally seen it nibbling the leaves at night, the 
caterpillars of the Tiger Moth and the Small Yellow- 
underwing and some others are no doubt occasional 
hangers-on, there is a small brad-shaped yellow grub, 
probably of a fly, that I have found eating the 
immature seeds, and I once, but only once, saw some 
cuckoo-spit on a plant, for it was not there the next 
day. 
There are, however, two other well-known evils 
from which plants suffer: one of them is the galls of 
one sort or another that are more conspicuous on the 
leaves of our trees than on our herbaceous plants. 
Our Oaks and Beeches are often attacked by them, 
and the small flies that are hatched from them tempt 
me to say something about their natural history, but 
once again we must steer clear of the side issues. 
Galls, however, are to be found upon our herbaceous 
plants as well as upon the leaves of trees. 
The Speedwells, the Nettles, and the Wood-sage 
