Figure 12.

Distribution of F-dextrans after injection into rachilla sieve tubes. A, Considerable spreading to other vascular bundles occurred in the anastomosing connections immediately below the point of grain insertion on the rachilla (3-kD F-dextran). B, In the region of the xylem discontinuity in the pedicel, conducting sieve tubes surround the central core of modified tracheary elements (3-kD F-dextran). C, Unloading occurred from more sieve tubes compared with tracers injected into a grain sieve tube (70-kD F-dextran). ch, Chalaza.