In Hevea and Manihot, latex vessels are formed in an entirely different manner by the fusion of rows of cells derived from the cambium. These cells arise by the division of cambium cells in precisely the same way as any other cells of the inner bark. When first formed they are more or less brick-shaped. They are nearly square in section and their length is three or four times as great as their breadth. The particular cells which ultimately fuse to form the latex vessels are arranged in the form of a network which is generally one cell thick. The meshes of which the network is composed consist of one or two rows of cells, and are elongated in the direction of the length of the stem. The walls which intervene between the separate cells of the same network soon break down, and a more or less free passage is established throughout The interstices of the network are occupied by the medullary rays, which are groups of thin-walled cells running by way of the cambium radially from the bark into the wood. The medullary rays serve in part as conducting channels for food materials between the wood and the bark, and in part for the storage of reserve food supplies. The whole laticiferous system consists of a series of such networks one within the other, extending round the stem. The space between two adjoining networks is occupied by the cells and tubes of the phloem. From the arrangement of the laticiferous vessels it will be readily understood that their contents can flow more easily in the longitudinal direction than transversely round the stem.