Introduction

Just as the external appearance of living organisms — both plants and animals — shows structural similarities as well as variations, examining their internal structure reveals a similar mix of shared features and real differences. This chapter looks at the internal structure and functional organisation of higher plants; the study of a plant's internal structure is called anatomy. The plant body is built up in a hierarchy: the cell is the basic structural and functional unit, cells are grouped together into tissues, and tissues in turn combine to form organs such as the root, stem and leaf. Different organs of the same plant are not built alike internally — each organ's internal structure reflects the particular function it performs. Even within the flowering plants (angiosperms), the two major groups — the monocotyledons and the dicotyledons — turn out to be anatomically distinct from one another. Internal structure is also shaped by environment: plants growing in different habitats often show internal adaptations suited to those conditions. The sections that follow examine first how plant tissues are organised into tissue systems, and then how these tissue systems come together differently in the roots, stems and leaves of monocot and dicot plants.