The first step towards a quantitative observation is often the delineation of a classification scheme of some sort. This type of classification will often arise from a series of qualitative observations that have been carefully recorded and noted.
The classic example of classification is the binomial nomenclature developed by Carl Linnaeus for naming species (fully worked out and included in the 10th edition of Systema Naturae - 1758) .
In 1753 he published the first edition of Species Plantarum. This was a very substantial work (1242 pages in two volumes) that included all the plant species then known by Linnaeus. The prime importance of this book is that it is the primary starting point of plant nomenclature as it exists today.