Rubber is derived from a milky liquid, known as latex, which occupies a special series of channels in the cortex, or inner bark of a number of different species of plants. The proportion of rubber contained in the latex varies greatly in different species. In many latices rubber is almost or entirely wanting, its place being taken by various resinous substances. The majority of the plants in which the latex contains a large proportion of rubber are either trees, or shrubs, or woody climbers. Before considering the origin and functions of latex, we propose to describe in very brief outline the structure and functions of those parts of a woody plant or tree which are directly or indirectly affected when the latex is removed by the operation of tapping.