Definition - What does Columella mean?
The columella is a sterile dome-shaped structure on the tip of a sporangiophore, its function is to allow for nutrient exchange between the active protoplasm below and the developing spores inside the upper part of the sporangial head. So, within the spore case of mosses or sporangiophores, this columella is a sterile portion of tissue within the spore case outer layer that aids in nutrient exchange. The columella is typically located within the theca of various types of mosses.
MaximumYield explains Columella
The columella is surrounded by spore-producing cells. Cells which produce spores are known as archesporium. The columella also refers to story 1 and story 4 cells in the root cap located in the quiescent center. The quiescent center is a group of cells, up to 1,000 in number, situated in a hemisphere, located just behind the growing root tip of a plant. This region has very slowly occurring growth or even dormancy. The cells in this region are able to resume meristematic growth should the root tip or any other surrounding tissue become damaged for any reason.