On the third year after I had noticed the attendance of the ants on my passion-flower, I found that the glands were not so well looked after as before, and soon discovered that a number of scale-insects had established themselves on the stems, and that the ants had in a great measure transferred their attentions to them. An ant would stand over a scale-insect and stroke it alternately on each side with its antennae, whereupon every now and then a clear drop of honey would exude from a pore on the back of the latter and be imbibed by the ant. Here it was clear that the scale-insect was competing successfully with the leaves and sepals for the attendance and protection of the ants, and was successful either through the fluid it furnished being more attractive or more abundant.* (* I have since observed ants attending scale-insects on a large plant of Passiflora macrocarpa in the palm-house at Kew.) I have, from these facts, been led to the conclusion that the use of honey-secreting glands in plants is to attract insects that will protect the flower-buds and leaves from being injured by herbivorous insects and mammals, but I do not mean to infer that this is the use of all glands, for many of the small appendicular bodies, called "glands" by botanists, do not secrete honey. The common dog-rose of England is furnished with glands on the stipules, and in other species they are more numerous, until in the wild Rosa villosa of the northern counties the leaves are thickly edged, and the fruit and sepals covered with stalked glands. I have only observed the wild roses in the north of England, and there I have never seen insects attending the glands. These glands, however, do not secrete honey, but a dark, resinous, sticky liquid, that probably is useful by being distasteful to both insects and mammals. If the facts I have described are sufficient to show that some plants are benefited by supplying ants with honey from glands on their leaves and flower-buds, I shall not have much difficulty in proving that many plant-lice, scale-insects, and leaf-hoppers, that also attract ants by furnishing them with honey-like food, are, similarly benefited. The aphides are the principal ant-cows of Europe. In the tropics their place is taken in a great measure by species of Coccidae and genera of Homoptera, such as Membracis and its allies. My pineapples were greatly subject to the attacks of a small, soft-bodied, brown coccus, that was always guarded by a little, black, stinging ant (Solenopsis). This ant took great care of the scale-insects, and attacked savagely any one interfering with them, as I often found to my cost, when trying to clear my pines, by being stung severely by them. Not content with watching over their cattle, the ants brought up grains of damp earth, and built domed galleries over them, in which, under the vigilant guard of their savage little attendants, the scale-insects must, I think, have been secure from the attacks of all enemies.