Katherine Esau was a botanist whose genius lay in her profound understanding of plant tissue. Her textbook 'Plant Anatomy' became the 'bible' for botany students for over half a century. Her research focused on the phloem, the tissue that transports sugars in plants. She was the first to provide a detailed structural and developmental description of how viruses move through this tissue to infect the entire plant. Esau’s work combined high-level microscopy with developmental biology, earning her the National Medal of Science. Her career spanned over 60 years, and she continued to publish research well into her 90s, remaining a titan in the field of plant biology.