Plants, like most animals, have organs composed of different
tissues, which in turn are composed of different cell types. A
tissue is a group of cells, consisting of one or more cell types,
that together perform a specialized function. An organ consists
of several types of tissues that together carry out particular
functions. In looking at the hierarchy of plant organs,
tissues, and cells, we begin with organs because they are the
most familiar and easily observed plant structures. As you
learn about the hierarchy of plant structure, keep in mind
how natural selection has produced plant forms that fit plant
function at all levels of organization.