Slide 16: shows the second vascular tissue, phloem. The large, elongated sieve elements shown here are the actual conductive cells; they transport organic materials both up and down the plant body. Sieve elements are living cells, and very sensitive to manipulation. When this slide was made the cytoplasm and proteins contracted and accumulated at one end of the cell, forming a "plug" (the triangular reddish areas in the center of the slide). Note the sieve plates. We shall learn more about the sieve elements in Unit 5.