At Figs. B, B 1, B 2, the same process is shown in the case of a small wild pea.
It is, however, certain that though a few individual seeds may sprout in the nests from time to time either with or without the concurrence of the ants, the great mass remain for many weeks, or even months, quite intact, neither decaying nor germinating, whereas every one knows that if a quantity of seeds are placed in the soil in a moist and warm place, all the seeds that are of one kind will almost simultaneously begin to grow after the lapse of a fixed interval.
Now if this took place in an ant's nest, the provisions would have to be rapidly consumed at stated periods and to be frequently renewed; but this is not the case. This is easily shown by an examination of the seeds contained in the nests in April or May, many of which will prove to belong to plants which fruit in the autumn and are not to be found later than November. Thus, for example, on May 5th at Cannes, I discovered nutlets of Cynoglossum pictum, which can scarcely have been collected later than the preceding October or November. Besides, during the time from the middle of January to the middle of March, scarcely a seed is collected under ordinary circumstances, there being extremely few wild plants in fruit at that season, and yet the granaries will be found well filled if a nest is opened at the end of this period.
A knowledge of the fact that ants in warm climates accumulate large and very varied stores of seeds retaining their power of germination, might at times be of service to travellers, by enabling them to obtain, by a stroke or two of the spade, an interesting collection of the seeds and the seed-like fruits of the country, when time and opportunity failed for obtaining them in a more satisfactory manner. The following list of plants, the grain, seeds, and small dry fruits of which I have found in the subterranean granaries of Atta structor and A. barbara, especially the latter, shows that the ants probably collect almost indiscriminately from any fruiting plant that falls in their way.
Fumitory (Fumaria, three species), honeywort (Alyssum maritimum), narrow-leaved sun rose (Fumaria viscida and F. Spachii), Oxalis corniculata, Silene, Linum gallicum, mallow (Lavatera cretica?), medick (Medicago), wild lentil (Ervum), spiny broom (Cytisus spinosus), Valerianella carinata, Centaurea aspera, Odontites lutea, Calamintha Nepeta, Polygonum convolvulus and P. aviculare, amaranth (Amaranthus Blitum and patulus), pellitory (Parietaria), Euphorbia, pine (Pinus), wild sarsaparilla (Smilax aspera), Setaria verticillata and S. italica, Andropogon Ischæmum, and of eight other plants of which I do not recognise the seeds. This list, comprising plants belonging to eighteen distinct families, might be greatly prolonged if I were to add to it the names of the seeds which I have seen the ants carry towards their nests, but have not actually detected in the granaries. Thus I have seen trains of ants burdened with the long-beaked, spirally-twisted fruits of crane's bill (Erodium), and, as above mentioned, with capsules of chickweed (Alsine media) and shepherd's-purse (Capsella Bursa pastoris), with whole orange pips, and even haricot beans, seeds of the New Zealand veronica (V. Andersonii), of Silene pseudoatocion, and many other garden plants, also with nutlets of the plane tree and seeds of the cypress.
Pliny mentions[28] incidentally having watched the ants carrying away cypress seeds, and comments upon the fact that so small a creature should be able to interfere with the growth of such a noble tree.
[28] Pliny, Nat. Hist., xvii. 14, 3.
I have little doubt that the seed stores of the ants in botanic and other gardens, where rare plants are cultivated in southern Europe and in warm climates generally, contain samples taken from the fruits of a great many of the rarer and more interesting species as well as of the weeds and native plants. Indeed I have been told that this is the case by my friend Dr. Bornet, who complains of the depredations committed by the ants in the gardens of the Villa Thuret, at Antibes. They go so far as to plunder the seed bags which are hung from the branches of the trees and shrubs, unless these are securely closed and tied with string; they carry off wholesale the grass and anemone seeds,[29] which are scattered when the lawns are resown; and Dr. Bornet has seen the seeds of Acacia retinoides lie heaped up by the handful at the entrances of their nests, and disappear below after a few hours.
[29] Properly grass grain and anemone achenes.
M. Germain de St. Pierre has observed similar facts at Hyères, where he has detected large stores of cereals in the granaries of the ants, and considers that the robberies committed by these creatures are sufficient in extent to cause a serious loss to cultivators.