R.A. Crowson 
Classification and Biology [PDF ebook] 

Classification of plants and animals is of basic interest to biologists in all fields because correct formulation and generalization are based on sound taxonomy. This book by a world authority relates traditional taxonomic studies to developments in biochemical and other fields. It provides guidelines for the integration of modern and traditional methods and explains the underlying principles and philosophy of systematics. The problems of zoological, botanical, and paleontological classifi cation are dealt with in great detail and microbial systematics briefly.