"Vertical section of the leaf of Potamogeton or Pondweed, showing air cavities or lecunae l, and parenehymatous cells p, with granules." — Encyclopedia Britanica, 1893

Pondweed Leaf

"Vertical section of the leaf of Potamogeton or Pondweed, showing air cavities or lecunae l, and parenehymatous…