A Spiny Vesicle in Slime-Producing Cells of the Bean Root

Vesicles bearing a specialized layer associated with the outer surface of the bounding membrane have become widely recognized fine structural components since the first reports of their presence in animal cells (8, 13, 15). Presumably this morphological specialization of the vesicle, which usually takes the form of a hairy coating or an alveolate reticulum, is related to functional specialization, including selective absorption, transport, or fusion. In some instances it has been shown that these vesicles in animal cells are concerned in the selective accumulation and transport of protein (3, 7, 14). Perhaps the first clear demonstration of coated vesicles in plant cells was that by Berkaloff () in the brown alga, Himanthalia. Manton (10) has illustrated and discussed fringed vesicles occurring in the green alga, Stigeoclonium, as have Leedale et al. (9) in Euglena. In the author's laboratory, vesicles with an alveolate surface and a diameter of about 85 mp, including coat, have been observed in a variety of meristematic and differentiating cells in flowering plants and have been studied particularly in root hairs (2). The present paper describes the occurrence of vesicles of a new kind in plant cells. These vesicles are unusual in several respects: they possess a specialized surface layer of a type not previously reported for vesicles in plant or animal cells, they occur in aggregates in the cytoplasm, and they are restricted to one stage in the differentiation of particular kinds of cells closely related ontogenetically.