134 BRITISH PLANTS 
service the plant provides the resident ants not only with 
shelter, but with all the food they require. 
We have no conclusive example of myrmecophily in 
the British flora. The presence, however, of extra-floral 
nectaries suggests in some cases relations with ants. Ants 
on their way to plunder the flower are side-tracked by 
these offers of food. In the same way the honey-dew on 
the leaves of the lime and maple may serve to attract 
ants. What service the ants perform in return for this 
food is not clear ; they may possibly destroy the eggs of 
injurious insects. 
There is no line of demarcation between the symbiosis 
which benefits and the parasite that destroys, or the 
insects that merely rob. All alike must live, and even in 
symbiosis the friend may become a foe, and assume the 
privileges of a master instead of the rights of a partner. 
In many a case of symbiosis one of the partners is a 
parasite in disguise. 
