cross-section of an aerial root found in the mantle
of a tree fern reveals the central, star-shaped xylem.
As the aerial root developed, primary xylem grew from five
to nine different points. Metaxylem was then produced towards
center forming a star shape. Phloem tissue developed
between the arms of the star. Cortical tissue and air spaces
surround the xylem and phloem tissues. A sheath made of
sclerenchyma cells enclosed the cortex. The root epidermis
cells outside the rootlet proliferated to produce a dense
mass of parenchyma tissue that held the root zone together.
aerial rootlet pictured above comes from a permian-aged
Brazilian tree fern
The picture was taken at 30x. Below one can see the specimen
from which the micrograph was taken. To view a series
of images that zoom in on the individual rootlet visit
Brazil Gallery (slide 1) in the Permian section of our