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There are as many candidates for the protistan plesiomorph as there are protophyte phyla, since we cannot decide which phylum is plausibly ancestral to the others. Although a species of Chlamydomonas would be an excellent plesiomorph for the Chlorophycophyta, and a species of Euglena the plesiomorph for the Euglenophycophyta, we have no good evidence for deriving an euglenoid cell from a chlamydomonad cell or vice versa; and similarly for a chrysomonad or pyrrophycophytan (dinoflagellate) plesiomorph. All are equally good or equally bad as a protistan plesiomorph. This situation can be explained in two ways: (1) we have as many independent origins of the protophyta from the Monera as we have separate plesiomorphs, and (2) there was a unitary origin of the protophyta, but the rapid, tachytelic evolution, in going from the adaptive zone of the metabolically specialized Monera (prokaryotes) to that of the structurally complex Protista (eukaryotes), resulted in rapid adaptive radiation into various protophyte phyla. In both cases we can argue that many intermediate forms, i.e., those that are neither good prokaryotes nor good eukaryotes, were lost and, hence, there is a considerable evolutionary gap. We are trying to peer across this gap; we are trying to reconstruct, conceptually, a phylogenetic bridge. Our phylogenetic methods tell us to look for serial relations to bridge such a gap. But that may well be futile in terms of cellular structure. Researchers have been aware of the difference between prokaryotes and eukaryotes for decades and have looked in vain for intermediates or missing links. They may yet turn up as fossils, but it is questionable that the needed fine-structural detail will be preserved. The best remaining possibility is molecular data. We need to compare conservative or plesiosemic molecules in protophyte plesiomorphs with each other and with comparable molecules in the monerans. Some such comparisons have been made, as we will see. Before turning to them, it is worth mentioning the work of the German botanist Pascher, who was a profound student of the algae in the early part of this century.