Tubular systems present in bean leaf glands have been studied electron microscopically. Ordered arrays of small tubules (290 A in diameter) arise from the endoplasmic reticulum in early stages of gland development and remain connected to it. Subsequently larger tubules (560–660 A in diameter) appear among the smaller tubules and gradually replace many of them. The large tubules are not connected to the endoplasmic reticulum. They contain an electron dense material and their walls exhibit a patterned substructure. In older gland cells the bundles of large tubules run randomly through the cytoplasm. The relationship of the two types of gland tubules to conventional microtubules has been examined morphologically and experimentally. The small tubules have larger diameters and thicker walls than microtubules. Neither type of gland tubule is affected by low temperature or colchicine, or, in thin sections, by pepsin digestion. This suggests that these tubules are not closely related chemically to either cytoplasmic or ciliary microtubules. The two systems of tubules are closely associated with prominent protein vacuoles in the gland cells, but are not directly connected to them.