He proposed that there were groups or genera of plants. He said that each genus was composed of many species and that these were defined by similar flowers and fruits. This principle of organization laid the groundwork for future botanists. He wrote his important "Historia Plantarum" shortly before his death. At Malines, in Flanders he established and maintained the botanical gardens of Jean de Brancion from 1568 to 1573, and first encountered tulips. This approach coupled with the new Linnaean system of binomial nomenclature resulted in plant encyclopaedias without medicinal information called "Floras" that meticulously described and illustrated the plants growing in particular regions. The 17th century also marked the beginning of experimental botany and application of a rigorous scientific method, while improvements in the microscope launched the new discipline of plant anatomy whose foundations, laid by the careful observations of Englishman Nehemiah Grew and Italian Marcello Malpighi, would last for 150 years. More new lands were opening up to European colonial powers, the botanical riches being returned to European botanists for description. This was a romantic era of botanical explorers, intrepid plant hunters and gardener-botanists. Significant botanical collections came from: the West Indies (Hans Sloane (1660–1753)); China (James Cunningham); the spice islands of the East Indies (Moluccas, George Rumphius (1627–1702)); China and Mozambique (João de Loureiro (1717–1791)); West Africa (Michel Adanson (1727–1806)) who devised his own classification scheme and forwarded a crude theory of the mutability of species; Canada, Hebrides, Iceland, New Zealand by Captain James Cook's chief botanist Joseph Banks (1743–1820). By the middle of the 18th century the botanical booty resulting from the era of exploration was accumulating in gardens and herbaria – and it needed to be systematically catalogued. This was the task of the taxonomists, the plant classifiers. Plant classifications have changed over time from "artificial" systems based on general habit and form, to pre-evolutionary "natural" systems expressing similarity using one to many characters, leading to post-evolutionary "natural" systems that use characters to infer evolutionary relationships. Italian physician Andrea Caesalpino (1519–1603) studied medicine and taught botany at the University of Pisa for about 40 years eventually becoming Director of the Botanic Garden of Pisa from 1554 to 1558.