Stereoscopic scanning electron microscopy of the chromosomes in Vicia faba (broad beans).

Metaphase chromosomes of Vicia faba (broad beans) were observed in situ with a scanning electron microscope by cryofracturing the cell. The chromosome is composed of tortuous fibers 500 A in diameter. They may be seen distributed randomly, but sometimes they are seen running parallel in the chromosome. The parallel fibers spiral around the main body of the chromosome, whereas they run longitudinally in the secondary constriction. If a chromosome is composed of a single strand (unineme hypothesis for the chromosome), the parallel fiber arrangement may imply that a single fiber is looping back and forth in the chromosome.