Early Plants

Characteristics

Psilotum

Lycopodium

Selaginella

Ancient Lycopods

Equisetum

Ferns


Ancient forms of the Lycophytes

Why couldn't these lycopods get even larger, considering the relatively mild and moist environmental conditions? A simple case of division in one versus two planes. In these early trees, the xylem cells could only divide parallel to stem edge...thus each cell layer formed was larger and eventually weaker as most of it was open space once the cellular contents died . In the gymnosperms cells could divide in both a parallel direction and at right angles to fill the gaps with expanding stem size. With smaller cells and more wall material the wood become stronger.

For more on these ancient forests visit the pages on fossil plants listed on the syllabus...