"Open" minor vein (derived)

Plasmodesmatal fields present

Transmission electron micrograph of an "open" type of leaf minor vein in which companion cells are symplastically connected with each other and with other parenchyma cells of the leaf by numerous plasmodesmata aggregated in fields (find one at the top, one near the bottom, and two in the central region of the micrograph). The smaller micrograph shows a plasmodesmatal field in detail.

Four sieve elements (note their thick walls with little or no contents shown) are present, and the companion cells are somewhat darker in their protoplasmic contents which are not vacuolated. Phloem parenchyma cells have lighter appearing contents, and are somewhat vacuolated. From cottonwood (Populus deltoides).