Figure 24

"A diagram showing the evolutionary levels of the various algal groups and the mutational activity within each group" from The Algae and their Life Relations. Fundamentals of Phycology by Josephine E. Tilden (University of Minnesota Press, 1937)." The most recently evolved members of the group (Chroococcaceae, Bangiales, Ectocarpales, etc.), shown nearest the center line, are the simplest in form and structure and represent most closely the ancestral type in each case. The oldest or earliest evolved members of the group (Stigonemataceae, Ceramiales, Fucales, etc.), shown farthest from the center, are the most specialized, having undergone, through mutational variations, a more or less complete change from the ancestral type." (Tilden 1937:5). The figure shown is Plate II, page 40; used by permission of the University of Minnesota Press.