variety of branching patterns to expose them to as much sunlight as possible to
maximize photosynthesis. Competition for light was of primary importance to
the evolution of land plants. Those that developed the most efficient branching
patterns gathered the most light and,therefore, were the most successful.
As plants grew larger, they progressed from random branching to tiers of
branches to achieve greater efficiency with a minimum of self-shading similar to
present-day pines.This added weight increased the mechanical stress on the plant,
requiring stronger branches to prevent limbs from breaking during storms.These
innovations gave rise to the preponderance of floras in existence today.
THE REEF BUILDERS
Silurian marine invertebrates (Fig. 80) were intermediate in evolution
between Ordovician and Devonian lines.The Silurian is paleontology’s “dark
Figure 79The scale tree
was one of many early
trees in the lush
Carboniferous forest.SILURIAN PLANTS