In the great abysses of the ocean, where vegetable life is absent, the strange creatures which live there in utter darkness prey upon others, and they again on others which belong to lesser depths, the ultimate source of life being again the minute surface organisms which, possessing chlorophyll, can make organic out of inorganic substances by the energy obtained from sunlight. Thus only is life made possible in the green hells of the sea Where fallen skies and evil hues and eyeless creatures be. On the land, the dependence of animals on plants is in large measure direct, as the supply of vegetable food is abundant and widespread. The largest land animals are all vegetable feeders; so are the majority of our own native mammals, and in a great measure our birds; while most of the creatures upon which the flesh-eating animals prey are themselves vegetable feeders. The distribution of land animals over the globe is thus dependent in large measure on the distribution of plants. On account of the profusion and variety of plant life, and the fact that most vegetable feeders can thrive on various sorts of plants, few animals are restricted in their range by the presence or absence of any particular species or genus, but complete dependence of this sort is by no means unknown. The larvæ of some Butterflies, for instance, eat the leaves of one plant only; the Peacock (_Vanessa io_) and the Small Tortoiseshell (_V. urticæ_) are cases in point. The caterpillars of both these species feed exclusively on the Common Nettle (_Urtica dioica_). Should the efforts of farmers and gardeners succeed in exterminating this unwelcome plant, these two butterflies would disappear from the Earth. Sometimes absolute mutual dependence is found on both the animal and vegetable sides. The American _Yucca filamentosa_, often grown in our gardens, depends solely on the little moth _Pronuba yuccasella_ for its pollination, just as the insect is absolutely dependent on the plant (see p. 80), and other species of Yucca have each its particular dependent moth, which feeds on no other plant, and whose flowers are pollinated by no other. Apart from such special cases, the general dependence of animals upon plants is obvious, and is by no means confined to food-supply. Animals of all grades, from human beings to Caddis Worms, construct houses of vegetable materials; trees are the chosen home of large sections of our fauna, and the herbs of the field are the world for millions of tiny beings. There’s never a leaf or a blade too mean To be some happy creature’s palace.