Fig. 8.2-2. Magnification of sieve tube member of milkweed. This micrograph shows the sieve plate at high magnification; its tilt is obvious, as are the bent ends of both sieve tube members. Notice that the cells on the left are all short, block-shaped and have protoplasts, so they are obviously not sieve tube members. They are also too large to be companion cells (they also do not contact sieve tube members). The two long cells on the right have the empty appearance of sieve tube members, but without being able to examine them for tilted sieve plates or bent ends, we cannot be certain from this photo. The arrows point to several narrow, cytoplasmic cells that are in contact with sieve tube members. They appear to be companion cells.