The first 45 chapters of the German "Botany Online" "have been translated into English covering all plant anatomy, classic genetics, organic chemistry and plant biochemistry, intercellular communication, interactions between plants, fungi, bacteria, and viruses, evolution, and a part of ecology." An index to the textbook provides A-Z access to topics. Illustrations are included. In addition, this amazing site serves as a portal to many, many other resources on the web, provides full-text online to biology classics, provides links to online education in botany, and much, much more.
Link to resource: Botany Online: The Internet Hypertextbook