The latex of the rubber tree is manufactured and contained in a network of capillary tubes as thin as a third of a human hair and extensively present in the external phloem tissues of the plant so that in each tree about a million meters of such tubes form the reservoir from which latex flows out on tapping to yield something of the order of 5.7 × 109 litres of latex per year in Malaysia alone. After reviewing the structure of the latex vessel system and the development of early theories of latex flow, the author reviews modern theories brought about by the impact of newer knowledge of ultrastructure, colloidal properties and constituents of latex as they affect latex flow, lutoid damage, plugging of latex vessels and related subjects. The influence of drainage area on latex flow and the changes in latex flow induced by the use of stimulants in exploitation technology add further insight into the mechanisms of latex flow promotion. The subject matter of this monograph forms an essential part of the physiological research mounted in the RRIM to continue the struggle for achieving greater productivity of Hevea.