In vegetables, I grew three species of sweet potatoes--yellow, purple, and white skinned, and which differ also in their leaves and flowers; cabbages, kidney-beans, pumpkins, yuccas (Jatropha manihot), quequisque (a species of arum, Colocasia esculenta), lettuces, tomatoes, capiscums, endives, parsley, and carrots. The climate was too damp to grow onions; neither could I succeed with peas, potatoes, or turnips. Scarlet runners (Phaseolus multiflorus) grew well, and flowered abundantly, but never produced a single pod. Darwin has shown that this flower is dependent, like many others, for its fertilisation upon the operations of the busy humble-bee, and that it is provided with a wonderful mechanism, by means of which its pollen is rubbed into the head of the bee, and received on the stigma of the next plant visited.* (* "Gardener's Chronicle" October 24, 1857 and November 14, 1858; also T.H. Farrer in "Annals of Natural History" October 1868.) There are many humble-bees, of different species from ours, in tropical America; but none of them frequented the flowers of the scarlet runner, and to that circumstance we may safely ascribe its sterility. An analogous case has been long known. The vanilla plant (Vanilla planifolia) has been introduced from tropical America into India, but though it grows well, and flowers, it never fruits without artificial aid. It is the same in the hothouses of Europe. Dr. Morren, of Liege, has shown that, if artificially fertilised, every flower will produce fruit; and ascribes its sterility to the absence, in Europe and India, of some insect that in America carries the pollen from one flower to another.* (* Taylor's "Annals of Natural History" volume 3 page 1.) When those interested in the acclimature of the natural productions of one country on the soil of some distant one, study the mutual relations of plants and animals, they will find that in the case of many plants it is important that the insects specially adapted for the fertilisation of their flowers should be introduced with them. Thus, if the insect or bird that assists in the fertilisation of the vanilla could be introduced into and would live in India, the growers of that plant would be relieved of much trouble, and it might be thoroughly naturalised. Judging from my experience, it would be useless to attempt the acclimature of the scarlet-runner bean in Chontales unless the humble-bee were also introduced. Caterpillars, plant-lice, bugs, and insect pests of all kinds were numerous, and did much harm to my garden; but the greatest plague of all were the leaf-cutting ants, and I had to wage a continual warfare against them. During this contest I gained much information regarding their habits, and was successful in checking their ravages, and I shall occupy the remainder of this chapter with an account of them. LEAF-CUTTING ANTS.