THE STRUCTURE AND DEVELOPMENT OF AN UNUSUAL TYPE OF ARTICULATED LATICIFER IN MAMMILLARIA (CACTACEAE)

Although the laticifers of several species of Mammillaria can technically be classified as being of the articulated type, they differ significantly from all other reported articulated laticifers. They are derived from cells which differentiate only in older tissues, never in meristematic or young regions. The development involves the complete lysis of masses of cells, not just the perforation or resorption of the end walls in a single file of cells. At maturity, the laticifer lumen is lined with a one-to-several layered epithelium which may be quite thick. The laticifers increase in diameter with age, apparently by the lysis of the inner epithelial cells. Laticifers occur in the pith, cortex and tubercles of the vegetative body but were not observed in the roots, flower parts or in seedlings up to eight months old. Seven species were studied, all of which have “milky sap.” and the laticifers of each were virtually identical to the laticifers of the others.