MESSMATES, MUTUALISTS, AND PARASITES 83 



big stomata [i.e. pores in the epidermis] on the overlapping 

 scales of the still-closed heads in such quantities that one can 

 see a drop of it on every scale in the early morning, whilst 

 later in the day, as the water evaporates, little masses, or even 

 crystals, of sugar are to be found. This sugar, either in its liquid 

 or solid form, is very palatable to the ants, which habitually resort 

 to these heads during the period of its secretion. And to pre- 

 serve it for themselves they resent any invasion from outside. 

 If one of the aforementioned beetles appears they assume a 

 menacing attitude. They hold on to the involucral scales with 

 their last pair of legs and present their fore-legs, abdomen, and 

 powerful jaws to the enemy, as shown in the figure. Thus they 

 remain till the beetle withdraws, if necessary hastening its retreat 

 by squirting formic acid in its direction. Then they quietly begin 

 to feed on the honey again." 



Much has yet to be learnt about the relations between British 

 plants and insects in the present connection, and no undoubted 

 case of ant-guards has so far been described. Some of our 

 native trees, however, harbour mites that appear to discharge 

 defensive duties. Scott Elliot (in Nature Studies] thus speaks 

 of them: " 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 . . . 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 mite 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." The arrangement described is of special 

 interest, as it appears to be a case of animals defending a plant 

 against other plants lower in the scale. 



THE POLLINATION OF FLOWERS BY ANIMALS. Of all the 

 numerous kinds of relation between plants and animals none 

 has attracted more attention than the one now to be briefly de- 

 scribed. So much is this the case that, though of absorbing 

 interest, it is almost in danger of becoming hackneyed. But 



