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A historical survey of studies of seedling morphology and anatomy in the palm family is given. The traditional three germination types—adjacent ligular, remote ligular, and remote tubular—that have been commonly recognized are reevaluated. The study includes seedlings of 63 species, representing the six subfamilies of palms. Morphological characteristics of germination patterns and the anatomy of the eophyll are described. The results of this survey show that germination types determined by the length of the hyperphyll (cotyledonary petiole) are not completely valid. Instead, a combination of characters such as primary root orientation, coleoptile length, number of cataphylls, and eophyll plication correspond to the most recent classification of the family, and represent a better way of describing germination.
The major ultrastructural and pigment characteristics of three chlorophyll b-containing photosynthetic prokaryote genera, Prochloron, Prochlorothrix, and Prochlorococcus, are summarized. Aspects of their ecology are reviewed, as are also the major findings of comparisons among the three genera, and between them and the cyanobacteria, based on analyses of nucleotide sequences. The information summarized is discussed to assess how closely the three genera are related and whether they form a natural taxonomic grouping within the cyanobacteria. It is concluded that, although much of the evidence points to substantial differences among the three genera, the convenience of keeping them together as a group, namely, Oxychlorobacteria (formerly Prochlorophyta), outweighs certain inconsistencies revealed by analysis of a range of objective criteria. Current views on the possible significance of the group to considerations of the evolution of green chloroplasts are also presented.