DEFENCE. I I I 



stipules of Vicia septum and Vicia sativa^ on the sepals 

 of the Paeony and by special hairs on the young leaves 

 of the Ash. It has not, however, yet been shown that 

 they keep off any special insect enemy in Britain. The 

 Bracken leaves, when young, have also many sugary 

 hairs which are visited by ants ; and, according to one 

 observer, these keep off caterpillars from the young 

 leaves. There are, however, in Britain " police '' 

 insects, which probably are of great importance to the 

 leaves they inhabit. Almost any common tree, such as 

 the Lime, Ash, Elm, or Horse-chestnut, will show on the 

 lower side of the leaves little hairy patches which occupy 

 the forks of the veins. If these are examined in summer 

 with a strong magnifying glass, and stirred up with a 

 pin, very small active insects or mites will be found. 

 They run about quickly, and once seen, can be observed 

 with ease, whenever looked for. The hairy grottoes 

 which they inhabit, are often rather neatly formed ; but 

 they are difficult to describe. As a rule the colour of 

 the insect is that of the hairs amongst which it lives. 

 These mites come forth at night, and appear to live 

 upon bacteria and upon the spores of fungi, lichens, or 

 algae. But here again, it is not possible to give as exact 

 details as would be desirable. 



A very extraordinary case has been described recently, 

 in which a plant and three kinds of insects are concerned. 

 Quercus pubescens is subject to the galls of a little insect, 

 Cynips argentea. These galls secrete nectar which 

 attracts ants, and these latter keep off caterpillars and 

 snails. 



Some idea can be gathered from the preceding pages 

 of the multifarious dangers to which plants are exposed. 

 The " Green-fly " or Aphid family are perhaps the 

 worst enemies. A single one of these creatures will in 



