The study of plants has been of absorbing interest to mankind since the earliest times. It is, moreover, one of his oldest and most fascinating fields of intellectual enquiry. During the prehistoric era, when still a nomadic hunter-gatherer, man began to discover which plants were of particular value. In time, as he settled and farmed, it became necessary to organize and codify this learning so that it could be passed on to succeeding generations and hence this essential wisdom was recorded for reference.