Crosswise cells or rays are typical but often hidden components of the vascular tissue in plans. Fossil plants occur in the shale layers below the Brush Creek limestone. These sometimes preserve incredible detail, including detailed carbon films from plants living over 300 million years ago. While shale plant fossils are excellent, I also find plant fossils in limestone. When found, they are usually gold in color, perhaps made of the mineral pyrite or marcasite.

These are a rare find here. Having woody plant material fall into the sea, sink into the sediment, and achieve preservation is unlikely. But it does happen. The three specimens I have found to date are all gold in color.

Preservation shows Crosswise cells.

Looking at the specimens under a microscope reveals preserved vascular tissue. The orientation for most is in the direction of growth, but many are in a perpendicular direction. These rays or crosswise oriented cells help support the growth structure of the other cells and help move food and water deeper into the wood. They also provide more strength and flexibility.

Microscope Photography of the Cells

I photographed the following specimens at several different depths and combined them into one focus-stacked image.

Limestone preserved woody plant material showing vascular tissue oriented in vertical and horizontal positions. This material is pyrite or marcasite and appears as a brighter gold color when first exposed to air. Scale bar = 1 cm.
CG-0426—Limestone preserved woody plant material showing vascular tissue oriented in vertical and horizontal positions. This material is pyrite or marcasite and appears as a brighter gold color when first exposed to air. Scale bar = 1 cm.
Specimen with additional zoom. The crosswise structures are easier to see.
CG-0426—Specimen with additional zoom. The crosswise structures are easier to see.
Specimen with even more zoom. Both vertical and horizontal vascular plant structures are easily visible here.
CG-0426—Specimen with even more zoom. Both vertical and horizontal vascular plant structures are easily visible here.
Another piece of the same specimen. Vascular cells in the direction of growth and additional crosswise cells can be seen. As the specimen broke, multiple layers were exposed. The lighter dots are unknown structures. Scale Bar = 1 cm.
CG-0426—Another piece of the same specimen. Vascular cells can be seen in the direction of growth and other crosswise cells. As the specimen broke, eroding material exposed multiple layers. The lighter dots are unknown structures. Scale Bar = 1 cm.

References