...[T]here are few indeed except trained naturalists who realize that any but a quite casual and superficial relation exists between these woodland toadstools and the trees under which they appear, or have carried their observations a stage further and noted the regular coincidence of certain kinds with particular tree species. The association between the toadstool-producing fungi of woodlands and our common trees is only one of many unlikely ways in which plants belonging to widely different groups are interrelated with one another and with the mechanism of life as a whole. Because this is so, and because there is a widespread and somewhat surprising lack of curiosity about the jigsaw puzzle formed by the different kinds of life that surround us in nature; about the interplay and interdependence of their various vital activities and the pattern formed when these are fitted together...it has seemed worth while to write this little book. (From the Introduction)