The ‘Isagoge Phytoscopica,’ a system of theoretical botany, very concisely written and in the form of propositions arranged in strict logical sequence, was a more important work and had more lasting effects upon the history of botany. We must look more closely into the contents of this volume, because it contains the foundation of the terminology of the parts of plants subsequently established by Linnaeus. Since the matter of the ‘Isagoge’ is produced in Ray’s ‘Historia Plantarum’ in italics, with special mention of the source from which it is derived, it cannot be doubted that Linnaeus had made acquaintance with the teaching of Jung as a young man, in any case before 1738. It is as important as a matter of history to know that Linnaeus’ terminology is founded on Jung, as it is to learn that his most general philosophical propositions on botanical subjects are to be traced to Cesalpino. It will moreover be fully shown in the account of the doctrine of sexuality that his knowledge of that subject was derived from Rudolf Jacob Camerarius. The first chapter of the ‘Isagoge’ discusses the distinction between plants and animals. A plant is, according to Jung, a living but not a sentient body; or it is a body attached to a fixed spot or a fixed substratum, from which it can obtain immediate nourishment, grow and propagate itself. A plant feeds when it transforms the nourishment which it takes up into the substance of its parts, in order to replace what has been dissipated by its natural heat and interior fire. A plant grows when it adds more substance than has been dissipated, and thus becomes larger and forms new parts. The growth of plants is distinguished from that of animals by the circumstance that their parts are not all growing at the same time, for leaves and shoots cease to grow as soon as they arrive at maturity; but then new leaves, shoots, and flowers are produced. A plant is said to propagate itself when it produces another specifically like itself; this is the idea in its broader acceptation. We see that here, as in Cesalpino, the idea of the species is connected with that of propagation. The second chapter, headed ‘Plantae Partitio,’ treats of the most important morphological relations in the external differentiation of plants; here Jung adheres essentially to Cesalpino’s view, that the whole body in all plants, except the lowest forms, is composed of two chief parts, the root as the organ which takes up the food, and the stem above the ground which bears the fructification. Jung, too, draws attention to the meeting-point of the two parts, Cesalpino’s ‘cor,’ but under the name of ‘fundus plantae.’