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Takebayashi and Morrell present an interesting review paper that attempts to test G. Ledyard Stebbins' hypothesis that selfing is an evolutionary dead end and sum up the current state of knowledge of mating system evolution. They specifically focus on the evolution of selfing and the various macroevolutionary approaches now being used to study evolutionary transitions. In applying likelihood ratio tests to the question of whether selfing is reversible they find that the current data sets are too small for the test. (see p. 1143)

Twice coiled and built to move: a complex sperm cell

Renzaglia et al. provide the first detailed description of the sperm cell of Psilotum nudum, a phylogenetically intriguing plant taxon. This complex male gamete is sinistrally coiled for approximately two revolutions and has an anterior locomotory apparatus with approximately 36 posteriorly directed flagella. A broad nucleus occupies most of the cell, and a spline (band of approximately 190 microtubules) beneath the plasmalemma binds the outer cellular coils and partly wraps the nucleus, forming a nuclear groove for most of the cell length. This complex architecture and lack of features associated with any yet-examined taxon suggest that Psilotum is an early divergent fern. (see p.1151)

Probing the red algae

Wattier et al. present the first unequivocal report of both intraspecific and intrapopulational cpDNA-RFLP polymorphism in the algae, specifically in the common red algal genus Ceramium. In C. virgatum, they found four haplotypes in five populations from three locations, with a mean of 2.26 ;pm 0.36 haplotypes per population, which is in the center of the range found in land plants using similar techniques. They emphasize the usefulness of this technique for the red algae over the more widespread PCR-based methods. (see p. 1209)

Stomatal index, Gingko, and CO₂

Chen et al. show that Gingko biloba is a reliable nearest living equivalent (NLE) taxon for predicting CO₂ levels in the environment through comparison of living and fossil stomatal characters. The leaves have a high fossilization potential and are abundant in the fossil record from the late Triassic to the present. Chen et al. studied five sources of natural variation in the stomatal density and index of Gingko biloba and show that this variability was considerably less than the difference in leaf stomatal density and index between modern and fossil samples. The stomatal indices of four fossil Gingko species indicate that there was a relatively high CO₂ concentration in the Mesozoic. (see p. 1309)

This Article Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Search for Related Content