Authorized in 1786 by king Carlos III, Spain made a botanical expedition in the viccroyalty of New Spain exploring Mexico, the West Indies, northern Central America, Baja and Alta California and Nootka (near Vancouver, Canada) under the command of Martin dc Sesse y Lacasta and (from 1790) Jose Mariano Mocino. The order by the king was to establish a botanical garden and a scientific expedition 'to make drawings, collect the natural products, and illustrate and complete the work of doctor Francisco Hernandez' (Rickett, 1947). In the 16th century Hernandez was one of the first scientists to visit the new world.

The expedition was formally 'incorporated' in August 1787, finding and preparing a site for the botanical garden was the first thing to do; later Sesse begun his exploration, starting in the Valley of Mexico.

Sesse (1751-1808), a doctor from Aragon, Spain, living in Mexico, became director of the botanical garden in Mexico City and conceived the idea of the expedition, also acting as the head of it; Mocino (1757-1820), a Mexican-born physician and student of botany of Spanish descent, joined the expedition in 1790 replacing some other member. They returned to Spain in 1803 where Mocino took refuge in Scssc's house. After Scsses death in 1808 it was Mocino who tried to keep the project of producing a Flora Mexicana alive. This flora however never materialised. But an extensive literature on the Botanical Expedition has been published later, see the list of selected literature.

Collections were made in the field of botany and zoology, resulting in a herbarium and a large number of illustrations executed by a number of artists.

Part of the collection of these drawings is now known as the Torncr Collection of Sesse and Mocino Biological Illustrations. It comprises 1989 watercolor drawings and sketches; about 1800 are of botanical subjects and the remainder are of various animal species. In 1981 this collection was purchased by the Hunt Foundation and in 1998 a CD-ROM was produced with the drawings (White et al., 1998). Rogers McVaugh (1909-2009), authority on the Sesse and Mocino expedition, wrote the historical introduction; this CD is no longer available but the contents can be viewed now on the website of the Hunt Institute for Botanical Documentation (HIBD).

Almost all of the drawings were made between 1787 and 1799, during a series of long 'excursiones' as they were called; they arrived in Madrid in 1803. In the wake of the retreating army of Napoleon in 1812 they were transferred to Montpellier in France; here and later in Geneva they were studied by Swiss botanist Augustin Pyramus dc Candolle from 1813 to 1817. He found the illustrations more useful than the descriptions made by Sesse and Mocino. De Candolle also resided in Montpellier at the time when Mocino arrived there from Madrid; Mocino had been working under the French occupation regime (1808-1813) in Spain.

De Candolle returned to Geneva in 1816 and, with the permission of Mocino, took with him the drawings. Previously the collection had...