Fig. 7.2-13. Transverse section of cosmos (Cosmos) stem. These vessel elements are interconnected by circular bordered pits, visible here in transverse section. Compare this view to the large circular bordered pits in pine (Fig. 7.2-11) or to the scalariform pits of grape (Fig. 7.2-12a). We can tell that these must be circular bordered pits because they do not extend all the way across the contact face: the arrows indicate the individual pit chambers, and between each arrow are the borders of the pits.

            This is not really an easy view for beginners to see. You have to examine your slides carefully at high power (a 25x or 40x objective), and the sections must have been cut well to give a clean surface. However, with just a little practice, it is not too difficult to see this beaded appearance. You need to worry about this only if you are examining a tissue transverse section and want to determine if a cell is a fiber of a tracheary element: if there is any beaded appearance to the wall at all, it must contain bordered pits. Fibers will have very narrow pits that are either definitely much more slender than these or so slender you almost cannot see them if the wall appears completely uniform, it probably is a fiber.