cambium

noun3

1. •
   A layer of cells between the xylem and the phloem that is responsible for the secondary growth of roots and stems.

   • During winter we perceive no change in the cells of the cambium layer, which are filled with nutritive matter […]. — 1863
2. •
   Periosteum, a membrane that covers the outer surface of bones
3. •
   (no longer used) One of the humours formerly believed to nourish the bodily organs.

   • The radical or innate is daily supplied by nourishment, which some call cambium, and make those secondary humours of ros and gluten to maintain it […] — 2001