The question of the Lusitanian and American elements in our flora has been treated at some length both because it offers one of the most interesting problems in British botany, and because it affords a good illustration of the far-reaching nature of the questions which may lie behind the occurrence on our hills or in our valleys of even the humblest plant or animal. Each organism has a long record behind it, stretching far beyond the earliest periods of human history; and it is only by wide and patient study that we can hope to trace any portion of its story. CHAPTER VIII SOME INTERESTING BRITISH PLANT GROUPS In the preceding chapters glimpses have been obtained of some of the wider aspects of plant life, particularly as seen on the hills and plains of our own country. The species composing our flora have been seen mostly, not as individuals, but as portions of regiments and armies, particular plants being mentioned but seldom, where required for purposes of illustration. In the final chapter it will be well to abandon this collective treatment, and glance at a few individual species or genera or small natural groups which possess features of interest of one sort or another. No systematic arrangement need be attempted: it will be pleasanter to ramble on, allowing our points of inquiry to turn up as they might on a country walk. A consideration of abnormalities in the manner in which plants obtain their food-supply--irregular nutrition, as it has been called--will raise some interesting questions, and will bring us up against some of the most remarkable species which are found in the British flora. The outlines of the method by which plants manufacture their food are familiar to all, and have been referred to already (pp. 75, 132). The roots absorb from the soil water containing dissolved salts, which is passed up by the stems into the leaves. The leaves extract from the air carbon dioxide. The chlorophyll, or green colouring-matter of the leaves, possesses the remarkable power in the presence of sunlight of breaking up and recombining these substances into the compounds which go to build up the plant-body. As has been pointed out, it is this power of forming organic out of inorganic matter that especially distinguishes plants from animals. But not all plants manufacture their food in this way. A large number feed like animals, finding their sustenance sometimes in living, more often in dead, organic material, either animal or vegetable. The whole enormous group of the Fungi do not possess chlorophyll, and in consequence are dependent on organic materials for their food. Some of the most familiar of the lower Fungi live on cheese, leather, bread, or any other damp animal or vegetable material. The higher forms, which decorate our woods and pastures, find their sustenance largely in leaf-mould. The groups of the Mosses, Hepatics, and Ferns, which are more highly organized than the Fungi, possess