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· MELASTOMÆ AND THEIR ANTS.
for I never found any along with the queen-ant. If the tree be shaken, the ants rush out in myriads, and search about for the molester. This case is not like the last one, where the tree has provided food and shelter for the ants, but rather one where the ant has taken possession of the tree, and brought with it the Coccidæ; but I believe that its presence must be beneficial. I have cut into some dozens of the Cecropia trees,
LEAF OF MELASTOMA.
and never could find one that was not tenanted by ants. I noticed three different species, all, as far as I know, confined to the Cecropice, and all farming scale-insects. As in the bull's-horn thorn, there is never more than one species of ant on the same tree.
In some species of Melastomo there is a direct provision of houses for the ants. In each leaf, at the base of the lamine, the petiole, or stalk, is furnished with a couple of pouches, divided from each other by the midrib, as shown in the figure. Into each of these pouches there is an entrance from the lower side of the leaf. I noticed them first in Northern Brazil, in the province of Maranham; and afterwards at Pará. Every pouch was occupied by a nest of small black ants, and if the leaf was shaken ever so little, they would rush out and scour all over it in search of the aggressor. I must have tested some hundreds of leaves, and never shook one without the ants coming out, excepting on one sickly-looking plant at Pará. In many of the pouches I noticed the eggs and young ants, and in some I saw a few darkcoloured Coccido or aphides; but my attention had not been at that time directed to the latter as supplying the ants with food, and I did not examine a sufficient number of pouches to determine whether they were constant occupants of the nests or not. My subsequent experience with the Cecropia trees would lead me to expect that they were. If so, we have an instance of two insects and a plant living together, and all benefiting by the companionship. The leaves of the plant are guarded by the ants, the ants are provided with houses by the plant, and food by the Coccido or aphides, and the latter are effectually protected by the ants in their common habitation.
Amongst the numerous plants that do not provide houses, but attract ants to their leaves and flower-buds by means of glands secreting a honey-like liquid, are many epiphytal orchids, and I think all the species of Passiflora. I had the common red passion-flower growing over the front of my verandah, where it was continually under my notice. It had honey-secreting glands Ch. XII.] USE OF HONEY.SECRETING GLANDS.
on its young leaves and on the sepals of the flower-buds. For two years I noticed that the glands were constantly attended by a small ant (Pheidole), and, night and day, every young leaf and every flower-bud had a few on them. They did not sting, but attacked and bit my finger when I touched the plant. I have no doubt that the primary object of these honey-glands is to attract the ants, and keep them about the most tender and vulnerable parts of the plant, to prevent them being injured; and I further believe that one of the principal enemies that they serve to guard against in tropical America is the leaf-cutting ant, as I have observed that the latter are very much afraid of the small black ants.
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 antennæ, 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, 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.
* I have since observed ants attending scale-insects on a large plant of Passiflora macrocarpa in the palm-house at Kew.
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 Coccidæ 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 Ch. XII.]
ANTS AND THEIR PROTÉGÉS.
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.
Many of the leaf-hoppers—species, I think, of Membracis—were attended by ants. These leaf-hoppers live in little clusters on shoots of plants and beneath leaves, in which are hoppers in every stage of development
-eggs, larvæ, and adults. I believe it is only the soft-bodied larvæ that exude honey. It would take å volume to describe the various species, and I shall confine my remarks to one whose habits I was able to observe with some minuteness. The papaw trees growing in my garden were infested by a small brown species of Membracis—one of the leaf-hoppers—that laid its eggs in a cottony-like nest by the side of the ribs on the under part of the leaves. The hopper would stand covering the nest until the young were hatched. These were little soft-bodied dark-coloured insects, looking like aphides, but more robust, and with the hind segments turned up. From the end of these the little larvæ exuded drops of honey, and were assiduously attended by small ants belonging to two species of the genus Pheidole, one of them being the same as I have already described as attending the glands on the passion-flower. One tree would be attended by one species, another by the other; and I never saw the two species on the same tree. A third ant, however-a species of Hypoclineawhich I have mentioned before as a cowardly species, whose nests were despoiled by the Ecitons, frequented all the trees, and whenever it found any young hoppers